Image forming method and ink composition

ABSTRACT

The present invention provides an image forming method and an ink composition whereby deterioration of a head plate, which is formed of silicon, is suppressed, and an image with higher precision is formed stably, the ink composition including an inorganic silicate compound and being ejected to form an image from an ink-jet head having a nozzle plate where a C 8 F 17 C 2 H 4 SiCl 3  film (fluorocarbon film) is provided on the surface thereof at a side toward the ink ejection direction of a nozzle.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 from Japanese PatentApplication No. 2009-218011 filed on Sep. 18, 2009, the disclosure ofwhich is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to an image forming method in which animage is formed by discharging an ink composition, and an inkcomposition used for the same.

2. Description of the Related Art

In recent years, as a result of ever-increasing demand for theprotection of resources, protection of the environment, enhancement ofoperational stability and the like, the conversion of inks into aqueousproducts has continued to proceed. The product qualities demanded fromaqueous inks include fluidity, storage stability, glossiness of film,clarity, coloring ability and the like, as in the case of oil-basedinks.

Since most pigments have significantly deteriorated aptitude such aspigment dispersibility with respect to an aqueous vehicle in comparisonwith the case of an oil-based vehicle, sufficient quality cannot beobtained by conventional dispersion methods. The use of variousadditives such as, for example, an aqueous pigment dispersion resin or asurfactant has been studied heretofore. However, an aqueous inkcomparable to an oil-based ink which has existing high quality andsufficient aptitude such as pigment dispersibility has not beenobtained.

With respect to these circumstances, for example, there is disclosed anaqueous ink composition which contains polymer particles and a coloranthaving a water-insoluble polymer coated thereon as a color material (forexample, see Japanese Patent Application Laid-Open (JP-A) No.2001-329199). Further, an aqueous inkjet recording liquid containing apigment and colloidal silica, an ink composition containing a resinemulsion and an inorganic oxide colloid, and the like are disclosed (forexample, see JP-A No. 9-227812, JP-A No. 9-286941, and Japanese PatentNo. 3550637), and a good image can be formed by including colloidalsilica or the like from the viewpoint of abrasion resistance, colorunevenness, clarity, and the like.

On the other hand, an inkjet recording method is also disclosed (forexample, see JP-A No. 9-286941), in which an ink composition is ejectedfrom a recording head having a plating layer containing a fluorine-basedpolymer on the surface of a nozzle plate. Further, there is disclosed anaqueous ink composition which prevents the elution of glass, silicon,silicon oxide, or the like in contact with an ink, by using the zetapotential of the ink and the zeta potential between a member and a colormaterial (for example, see JP-A No. 2003-165936).

SUMMARY OF THE INVENTION

According to an aspect of the invention, an image forming method and anink composition whereby deterioration of a head plate, which is formedof silicon, is suppressed, and an image with higher precision is formedstably, and wherein the ink composition includes an inorganic silicatecompound and is ejected to form an image from an inkjet head having anozzle plate where a C₈F₁₇C₂H₄SiCl₃ film (fluorocarbon film) is providedon the surface thereof at a side toward the ink ejection direction of anozzle, are provided.

BRIEF DESCRIPTION OF DRAWINGS

Exemplary embodiments of the present invention will be described indetail based on the following figures, wherein:

FIG. 1 is a schematic cross-sectional drawing showing one example ofinner structure of inkjet head.

FIG. 2 is a schematic drawing showing one example of the ejection portarrangement of the nozzle plate.

FIG. 3 is a plane perspective diagram showing one example of headstructure.

FIG. 4 is a magnified drawing magnifying and showing a part of FIG. 3.

FIG. 5 is a magnified drawing magnifying and showing a part of twodimensional nozzle arrangement (32×64).

FIG. 6 is a perspective diagram magnifying and showing a part of anotherexample of the head structure.

FIG. 7 is a plane perspective diagram magnifying and showing a part ofthe pressure chamber.

FIG. 8 is a cross-sectional drawing along line 9-9 of FIG. 7.

DETAILED DESCRIPTION

Among the conventional art described above, abrasion resistance of aformed image is improved in an aqueous ink composition containingpolymer particles, but it is difficult to say that the composition issufficient from the viewpoint of an ejection property. Further, when aninorganic oxide colloid is added in order to improve the image as inJP-A No. 9-286941 and when the added amount of the inorganic oxidecolloid is too much, the ink ejection property from the inkjet head maybe affected undesirably and the image quality may be damaged thereby.

On the other hand, when an inkjet head contacts with an ink, it is knownthat the ink tends to have an effect of causing the deterioration of anozzle plate which constitutes a head and a decrease in the liquidrepellent property of a liquid repellent film. However, a technique forforming higher quality image in which image forming properties such asthe ejection property are not damaged, and the liquid repellent propertyis also improved has not yet been successfully provided.

The invention has been made in view of the above circumstances, and anobject thereof is to provide an ink composition and an image formingmethod whereby decrease in the liquid repellent property of an inkjethead member is suppressed, and a more highly precise image can be formedstably. An aim of the invention is to achieve this object.

According to an aspect of the invention, when a nozzle plate of aninkjet head is formed of silicon, if a predetermined amount of aninorganic silicate compound is contained in the ink composition, thereis an effect of preventing decrease in the liquid repellent property ofthe liquid repellent film, in response to these circumstances by whichthe liquid repellent property of a liquid repellent film is reduced dueto the influence of the contact with the ink. In particular, it has beenfound that the effect is prominent in the case of using a structurewhere plural nozzles (ejection ports) are arranged two-dimensionally anda large amount of ink flows in the nozzles such that a highly preciseimage of, for example, 1200 dpi, or the like is obtained. The inventionhas been accomplished on the basis of this knowledge. Further, there isno case in which the ejection property is damaged during ink ejection.

Exemplary embodiments according to the aspect of the invention include,but are not limited to the following items <1> to <18>.

<1> An image forming method including ejecting an ink compositionincluding an inorganic silicate compound from an inkjet head having anozzle plate to form an image, the nozzle plate including a liquidrepellent film in at least a part, and the liquid repellent filmincluding a fluoroalkylsilane moiety.<2> The image forming method according to the item <1>, wherein theliquid repellent film including a fluoroalkylsilane moiety is formed byusing a compound represented by the following Formula (1):C_(n)F_(2n+1)—C_(m)H_(2m)—Si—X₃  Formula (1)

wherein, in Formula (1), n represents an integer of 1 or more; mrepresents an integer of 0 or more; X represents an alkoxy group, anamino group, or a halogen atom; and a part of X may be substituted withan alkyl group.

<3> The image forming method according to the item <1> or the item <2>,wherein the liquid repellent film is formed by chemical vapordeposition.

<4> The image forming method according to any one of the items <1> to<3>, wherein a content of the inorganic silicate compound in the inkcomposition is in a range of from 0.0005% by mass to 0.5% by mass withrespect to a total mass of the ink composition.<5> The image forming method according to any one of the items <1> to<4>, wherein at least a part of the nozzle plate includes silicon.<6> The image forming method according to any one of the items <1> to<5>, wherein the nozzle plate further includes a film which includes atleast one selected from the group consisting of a metal oxide, a metalnitride and a metal other than silicon.<7> The image forming method according to any one of the items <1> to<6>, wherein at least a part of the nozzle plate is provided with a filmwhich includes SiO₂ or tantalum oxide.<8> The image forming method according to any one of the items <1> to<7>, wherein the nozzle plate has plural ejection ports which eject theink composition, the inkjet head further includes plural pressurechambers respectively communicating with the plural ejection ports ofthe nozzle plate, plural ink supply flow paths respectively supplyingthe ink composition to the plural pressure chambers, a common liquidchamber supplying the ink composition to the plural ink supply flowpaths, and plural pressure generation units respectively deforming theplural pressure chambers, and an amount of change in volume within eachpressure chamber is controlled by driving the respective pressuregeneration unit to eject the ink composition.<9> The image forming method according to the item <8>, wherein thepressure generation units are piezo elements.<10> The image forming method according to the item <8> or the item <9>,wherein the plural ejection ports are arranged two-dimensionally in amatrix form.<11> The image forming method according to the item <10>, wherein theinkjet head forms an image at a drawing resolution of 1200 dpi or higherwith a single pulse ejection from the nozzle plate.<12> The image forming method according to any one of the items <8> to<11>, wherein the inkjet head further includes electrical wiring whichis arranged so as to penetrate the common liquid chamber and suppliesdriving signals to the pressure generation units.<13> The image forming method according to the item <12>, wherein thepressure generation units are disposed on the opposite side of thepressure chamber from a side thereof where the nozzle plate is arranged,and the common liquid chamber is disposed on the opposite side of thepressure generation units from a side thereof where the pressurechambers are arranged.<14> The image forming method according to any one of the items <1> to<13>, wherein the ink composition further includes a pigment, awater-soluble organic solvent, and resin particles.<15> The image forming method according to any one of the items <1> to<14>, wherein a pH of the ink composition is in a range of from 7.5 to10.0 at a temperature of 25° C.<16> The image forming method according to the item <14> or the item<15>, wherein the resin particles are self-dispersing polymer particles.<17> The image forming method according to any one of the items <1> to<16>, wherein the inorganic silicate compound is colloidal silica.<18> An ink composition including an inorganic silicate compound andbeing used for the image forming method according to any one of theitems <1> to <17>.

An image forming method of the exemplary embodiment of the invention isdescribed in detail below, and an ink composition is also described indetail through the description.

An image forming method of the exemplary embodiment of the invention isconstituted to include a process (hereinafter, refer to “ink ejectionprocess”) wherein the ink composition containing an inorganic silicatecompound is ejected from the ink-jet head having the nozzle plate wherethe liquid repellent film is provided in at least a part to form animage, and can be constituted to provide another process, if necessary.The exemplary embodiment of the invention further preferably has aprocess (hereinafter, “treatment liquid applying process”) which appliesa treatment liquid to be able to form an aggregate upon contact with theink composition on a recording medium.

In the exemplary embodiment of the invention, the ink composition isconstituted by containing the inorganic silicate compound, whichcontacts with the nozzle plate where the liquid repellent filmconsisting of a film containing fluoroalkylsilane is provided in atleast a part of the inkjet head, and thereby the liquid repellentproperty of the liquid repellent film is prevented from being reducedwhile having a good ejection property.

Therefore, an occurrence of the ejection defect due to changing the sizeof the ink droplet, the ejection rate or the ejection direction duringejection, or the like is suppressed, and thereby a high quality imagecan be formed stably. The effect of suppressing the occurrence of theejection defect becomes prominent when a part of nozzle plate is formedof silicon. That is to say, when a part of nozzle plate is formed ofsilicon ink is penetrated in through, for example, a pinhole from theliquid repellent film, silicon which is located at the lower layer iseroded to easily cause deterioration. However, in exemplary embodimentsof the invention, a high quality image can be formed stably due tosuppressing the deterioration.

[Ink Ejection Process]

The ink ejection process uses an inkjet head which has a nozzle plateprovided with a liquid repellent film including a fluoroalkylsilanemoiety in at least one part thereof and an ink composition (hereinafter,simply referred to “ink”) including an inorganic silicate compound (acontent thereof in the ink composition is preferably in a range of from0.0005% by mass to 0.5% by mass with respect to a total mass of the inkcomposition) is ejected to form an image. In this process, the inkcomposition can be provided selectively on the recording medium and canform a desirable visible image.

Image recording utilizing the inkjet method can be performed,specifically, by supplying energy thereby ejecting a liquid compositionto a desired recording medium, that is, plain paper, resin-coated paper,paper used exclusively for inkjet recording described, for example, inJP-A Nos. 8-169172, 8-27693, 2-276670, 7-276789, 9-323475, 62-238783,10-153989, 10-217473, 10-235995, 10-337947, and 10-217597, films, commonuse paper for electrophotography, clothes, glass, metals, ceramics, etc.As the inkjet recording method suitable to the exemplary embodiment ofthe invention, a method described in JP-A No. 2003-306623, in columns(0093) to (0105) may be applicable.

The inkjet method is not particularly limited and may be of any knownsystem, for example, a charge control system of ejecting an inkutilizing an electrostatic attraction force, a drop on demand system ofutilizing a vibration pressure of a piezo element (pressure pulsesystem), an acoustic inkjet system of converting electric signals intoacoustic beams, irradiating them to an ink, and ejecting the inkutilizing a radiation pressure, and a thermal inkjet system of heatingan ink to form bubbles and utilizing the resultant pressure (BUBBLEJET(registered trade mark)). Examples of the inkjet method include a systemof injecting a number of ink droplets of low concentration, a so-called“photo-ink” each in a small volume, a system of improving an imagequality using plural inks of a substantially identical hue and ofdifferent concentrations, and a system of using a colorless transparentink.

In the exemplary embodiments of the invention, there is preferred amethod where a pressure generation unit (for example, piezo element)using the pressure pulse method is used, the pressure generation unit isdriven to control an amount of change in volume within each pressurechamber and thereby the droplet diameter of the ink composition to beejected from the nozzle is changed to eject the ink composition from thenozzle; and a method where the pressure generation unit is driven manytimes, to thereby control the number of droplets ejected from thenozzle, and plural droplets are combined before landing. In this case,it is more important to suppress erosion of the silicon portion of thenozzle plate due to ink. A multiple tone image can be stably recordedwith the ink composition of the exemplary embodiment of the invention.

The inkjet head used in the inkjet method may be either an on-demandsystem or a continuous system. The ejection system includes,specifically, for example, an electric-mechanical conversion system (forexample, single cavity type, double cavity type, bender type, pistontype, share mode type, and shared wall type, etc.), an electric-thermalconversion system (for example, thermal inkjet type, BUBBLEJET(registered trade mark) type, etc.), an electrostatic attraction system(for example, electric field control type, and slit jet type, etc.), andan electric ejecting system (for example, spark jet type, etc.) and anyof the ejection systems may be used.

Ink nozzles, etc. used for recording by the inkjet method are notparticularly limited but can be selected properly depending on thepurpose.

As an inkjet head, there are a shuttle type where a short serial head isused to record while scanning the head in the width direction of therecording medium and a line head type (single-pass type) where arecording device is arranged in correspondence with the entire area ofone side of the recording medium and the line head is used. Thesingle-pass type forms an image on the whole face of a recording mediumdue to an operation where a full line head and the recording medium arerelatively moved once, using the full line head which covers the wholearea of the recording medium. For example, the single-pass type isdescribed in JP-A Nos. 2005-96443, and 2005-280346. That is to say, thesingle-pass type can perform image recording on the whole face of therecording medium by scanning the recording medium in the directionorthogonal to the device arrangement direction of the full line head,and a transferring system such as a carriage which scans the short headis not necessary. Further, since a complicated scanning control of themovement of the carriage and the recording medium is not necessary andonly the recording medium is moved, a high recording rate can berealized in comparison with the shuttle type. The image forming methodaccording to exemplary embodiments of the invention can be applied toall these types; however, when the method is generally applied to thesingle-pass type, a high precise nozzle arrangement and high ejectionfrequency are required, and therefore suppression of erosion due to inkis more important. There is a large effect on the improvement ofejection precision due to ink composition of the exemplary embodiment ofthe invention and prevention of erosion due to contact of the ink withthe nozzle plate.

Furthermore, in the ink discharging (ejecting) step according to theexemplary embodiment of the invention, when a line method is employed,recording can be suitably performed not only using one type of the inkcomposition, but also using two or more types of ink compositions, bysetting the ejection (droplet ejection) interval between the firstejected ink composition (n-th color (n≧1), for example, the secondcolor) and the subsequently ejected ink composition ((n+1)-th color, forexample, the third color), at 1 second or less. According to theexemplary embodiment of the invention, by setting the ejection intervalat 1 second or less in the line method, an image having excellentabrasion resistance and suppressed occurrence of blocking can beobtained under high speed recording that is faster than thatconventionally obtained, while preventing the spreading caused by theinterference between ink droplets or mixed colors. Further, an imagehaving excellent hue and drawing property (reproducibility of fine linesor fine parts in an image) can be obtained.

The volume of a droplet to be ejected from the inkjet head is preferably0.5 to 12 pL (picoliter) from the viewpoint of obtaining a high preciseimage. Further, a method where plural ink droplet volumes are combinedto form an image is preferred with respect to correction of unevennessor stripes during formation of a highlight image. In this case, thevolume of the small droplets forming the highlight image is preferably0.5 to 4 pL, the volume of the medium droplets to be mainly used ispreferably 2 to 8 pL, and the volume of the large droplets to be used inthe correction of unevenness or stripe is preferably 6 to 12 pL.

(InkJet Head Having Silicone Nozzle Plate)

The inkjet head employed in the image forming method has a nozzle plate.At least a part of the nozzle plate contains silicone. FIG. 1 is aschematic diagram showing one example of an internal structure of theinkjet head.

FIG. 1 shows an inkjet head 200 having a nozzle plate 11 and an inksupplying unit 20 which is provided on a opposite side from the inkejecting direction of the nozzle plate. The nozzle plate 11 has pluralejection openings 12 through which inks are ejected.

As typically shown in FIG. 2, the ejector ports (nozzles) (32×64) arearranged two-dimensionally in the nozzle plate 11. The nozzle plate isformed in part or on entirely of silicon. A structure may be used wheresilicon is exposed within a nozzle port and on the surface of the inkdischarging direction side, which are preferably coated (or provided)with a film which contains at least one kind selected from the groupconsisting of metal (including silicon) oxide and nitride, and a metal(other than silicon).

Further, a deposited film (a liquid repellent film containingfluoroalkylsilane moiety) of fluoroalkylsilane by using C₈F₁₇C₂H₄SiCl₃as a film (hereinafter, referred to as “fluorocarbon film”) containingfluorocarbons is formed by chemical vapor deposition method on thesurface of the plate.

The fluorocarbon film can be formed by, for example, coating withfluorocarbon-based resin, chemical vapor deposition, eutectoid platingwith a fluorocarbon-based polymer or the like, or a water repellentprocess of a fluorine silane process, an aminosilane process, plasmapolymerization of a fluorocarbon, or the like.

A method forming the liquid repellent film of the fluoroalkylsilaneincludes the following methods.

As a first example, there is a method where a monomolecular film or apolymer film having a water repellent property is formed by reactingfluoroalkyl trichlorosilane of CF₃(CF₂)₈C₂H₄SiCl₃, or the like with basematerial (See Japanese Patent Application Nos. 2500816, 2525536). In thechemical formula, CF₃(CF₂)₈C₂H₄— represents a fluoroalkyl group, and—SiCl₃ represents a trichlorosilyl group. In this method, the basematerial where an active hydrogen is present on the surface is exposedto a solution in which a fluoroalkyl trichlorosilane is dissolved, andchlorosilyl group (—SiCl) is reacted with active hydrogen to form a Si—Obond with the base material. As a result, a fluoroalkyl chain is fixedto the base material through Si—O bond. Herein, the fluoroalkyl chainprovides the water repellent property to the film. The water repellentfilm is a monomolecular film or a polymer film according to the formingconditions of the film.

As a second example, there is a method where a porous base materialwhich impregnates a compound containing a fluoroalkyl chain such asfluoroalkyl alkoxysilane including CF₃(CF₂)₈C₂H₄Si(OCH₃)₃ or the like isheated under vacuum, and the compound is evaporated to provide a waterrepellent property in the surface of the base material (see JP-A NO.6-143586). In this method, there is proposed a method in which anintermediate layer of silicon dioxide, or the like is provided in orderto increase adhesiveness between a water repellent film and the basematerial.

As a third example, there is a method in which fluoroalkyl silane isformed by chemical vapor deposition on the surface of the base materialby using a compound such as fluoroalkyl trichlorosilane such asCF₃(CF₂)₈C₂H₄SiCl₃, or the like (see JP-A No. 2000-282240).

As a fourth example, there is a method in which oxide fine particlessuch as zirconia and alumina are formed on the surface of the basematerial, and then fluoroalkyl chlorosilane or fluoroalkyl alkoxysilane,or the like is coated thereon (see JP-A No. 6-171094).

As a fifth example, there is a method in which a mixed solution whichadds metal alkoxide to fluoroalkyl alkoxy silane is hydrolyzed,dehydrated and polymerized, and then this solution is coated and firedon the base material, to thereby form a water repellent film in whichmolecules having a fluoroalkyl chain in the metal oxide are mixed (SeeJapanese Patent Application Nos. 2687060, 2874391, 2729714, 2555797). Inthis method, the fluoroalkyl chain provides the film with a waterrepellent property, and the metal oxide provides the film with highmechanical strength.

Among these forming methods above, chemical vapor deposition included asthe third example is preferable.

In the case of the chemical vapor deposition, a container into whichfluorocarbon material such as fluoroalkyl silane has been put and asilicone substrate are put in an airtight container made from Teflon(Trademark) and the like, the whole airtight container is placed in anelectrical furnace and fluoroalkyl silane is evaporated by raising thetemperature, and thereby a molecule such as fluoroalkylsilane isdeposited on the surface of the silicon substrate, and thereby chemicalvapor deposition can be performed. Thus, by chemical vapor deposition,for example a monomolecular film of fluorinated alkyl silane can beformed on the nozzle plate. In this case, the deposited surface ofsilicon substrate is preferably hydrophilized. Specifically, for examplethe surface of the silicon substrate is washed by using ultravioletlight (wavelength 172 nm), and thereby organic impurities are removed toobtain a clean surface. At this time, the silicon surface isspontaneously oxidized to coat the surface with SiO₂ film, and thereforewater vapor in the air is adsorbed directly on the surface, and thesurface is coated with an OH group to become a hydrophilic surface.

Another embodiment of the chemical vapor deposition method includes themethod described below.

The liquid repellent film of fluorinated alkyl silane, for examplefluoroalkyl trichloro silane such as CF₃(CF₂)₈C₂H₄SiCl₃ and water vaporat low pressure is introduced into a CVD reactor and thereby can bedeposited on the uncoated outer surface of the base. The partialpressure of fluoroalkyl trichlorosilane such as CF₃(CF₂)₈C₂H₄SiCl₃ canbe set to between 0.05 to 1 torr (6.67 to 133.3 Pa) (for example, 0.1 to0.5 torr (13.3 to 66.5 Pa)), and the partial pressure of H₂O can be setto between 0.05 to 20 torr (for example, 0.1 to 2 torr). The depositiontemperature can be set to between room temperature and 100° C. A coatingprocess can be performed using, for example, a Molecular VaporDeposition (MVD)™ machine from Applied Micro Structures, Inc.

The liquid repellent film of the exemplary embodiment of the inventionis a film formed by using fluorinated alkyl silane as the fluorocarbon.In particular, it is preferable to use the silane coupling compoundrepresented by Formula (1) below.C_(n)F_(2n+1)—C_(m)H_(2m)—Si—X₃  Formula (1)

In Formula (1), n represents an integer of 1 or more, and m representsan integer of 0 or more. X represents an alkoxy group, an amino group,or a halogen atom. Further, a part of X may be substituted with an alkylgroup.

Examples of the fluorinated alkyl silane include fluoroalkyltrichlorosilane such as C₈F₁₇C₂H₄SiCl₃ and CF₃(CF₂)₈C₂H₄SiCl₃, orfluoroalkyl alkoxy silane such as CF₃(CF₂)₈C₂H₄Si(OCH₃)₃,3,3,3-trifluoropropyl trimethoxy silane,tridecafluoro-1,1,2,2-tetrahydrooctyltrimethoxy silane,heptadecafluoro-1,1,2,2-tetrahydrodecyl trimethoxy silane, or the like.

In embodiments, a fluorocarbon film, which is a film formed by chemicalvapor deposition method using a silane coupling compound represented byFormula (1), is preferable.

In Formula (1), from the viewpoints of the liquid repellent property andthe durability of liquid repellent film, it is preferable that nrepresents an integer of 1 to 14, m represents an integer of 0 or 1 to5, X represents an alkoxy group or halogen atom; further, it ispreferable that n represents an integer of 1 to 12, m represents aninteger of 0 or 1 to 3, X represents an alkoxy group or halogen atom.

The thickness of liquid repellent film is not particularly limited, butis preferable in the range of from 0.2 nm to 30 nm, and is morepreferable in the range of from 0.4 nm to 20 nm. The thickness of liquidrepellent film has no particular problems in the range exceeding 30 nm,but when the thickness is 30 nm or less, it is advantageous from theviewpoint of uniformity of the film. When the thickness is 0.2 nm ormore, the water repellent property with regard to ink is good.

High quality image recording can be performed with a high resolution of1200 dpi by high speed single-pass (one pass of the recording medium)due to the nozzle plate. That is to say, plural nozzles of the nozzleplate are disposed two-dimensionally in a matrix form, and an ink supplyunit which is fixed to the nozzle has the flow path configurationallowing large volumes of ink to be ejected with high frequency (ejectedwith so-called high duty). Silicon, which is easily used in asemiconductor process, is used in part or in the whole in order toobtain a high precise image. Specifically, when a part or the whole ofthe nozzle plate is formed of silicon, for example, single crystalsilicon and polysilicon can be used as silicon. In the nozzle plateformed of silicon, erosion due to ink is recognized as a generalproblem, and erosion prevention using various protective films can beexamined. However, it is very difficult task to completely preventerosion of the nozzle plate due to ink resulting from defects, or thelike in the protective film, such as silicon oxide. In particular, asthe frequency of ink ejection, such as in the high speed single-passtype, is high and fresh ink readily contacts the silicon and theprotective film at all times, erosion of the silicon due to ink easilyproceeds. Further, in the high speed single-pass type where highprecision is required, there is high level of a demand for a response tothe deterioration of ejection precision due to ink erosion.

In embodiments, the ink composition to be used in ejection contains aninorganic silicate compound, and thereby the deterioration of the easilyeroded silicon can be effectively prevented.

The nozzle plates can be coated by forming a film which contains atleast one kind selected from the group consisting of metal (includingsilicon) oxide and nitride, and metal (excluding silicon). Specifically,when a part or the whole of the nozzle plate is formed of silicon, forexample, single crystal silicon and polysilicon. Further, when a part orthe whole of the nozzle plate is formed of silicon, for example, theremay be provided a film such as a metal oxide, for example silicon oxide,titanium oxide, chromium oxide, or the like or metal nitride such astitanium nitride, silicon nitride, or the like, or metal such aszirconium, on the single crystal silicon substrate. The silicon oxidemay be, for example, SiO₂ film formed by oxidizing the whole or a partof the silicon surface of the nozzle plate formed of silicon. A filmsuch as tantalum oxide (preferably, such as tantalum pentoxide (Ta₂O₅))or zirconium, chromium, titanium, glass, or the like may be formed on apart or the entirety of the silicon surface. Further, a part of thesilicon may be constituted to be replaced with glass (for example,borosilicate glass, photosensitive glass, quartz glass, soda-limeglass). A film consisting of tantalum pentoxide, or the like as well astantalum oxide has excellent ink resistance; in particular good erosionresistance with respect to alkaline ink is obtained.

An embodiment of the method forming the SiO₂ film is described. Forexample, SiCl₄ and water vapor is introduced into a chemical vapordeposition (CVD) reactor in which an uncoated silicon substrate isprovided, and thereby an SiO₂ film can be formed on the siliconsubstrate. After a valve between a CVD chamber and a vacuum pump pumpsout fluid and empties the chamber, the valve is closed, and SiCl₄ andH₂O vapor are introduced to the chamber. The partial pressure of SiCl₄can be set between 0.05 and 40 torr (6.67 to 5.3×10³ Pa) (for example,0.1 to 5 torr (13.3 to 666.5 Pa), and the partial pressure of H₂O can beset between 0.05 and 20 torr (for example 0.2 to 10 torr). Thedeposition temperature is generally between room temperature and 100° C.Further, in another embodiment, SiO₂ film can be formed on the siliconsubstrate by sputtering. The surface to be coated with SiO₂ film ispreferably cleaned before forming the SiO₂ film (for example, byapplying oxygen plasma).

The configuration example of the inkjet head including the nozzle platehaving plural ejection ports (nozzles) which are arrangedtwo-dimensionally is described in reference to FIG. 3 to FIG. 4. FIG. 3is a plane perspective diagram showing one example of the headstructure, and FIG. 4 is a magnified drawing magnifying and showing apart of FIG. 3.

In order to densify dot pitch recorded on the recording medium, it isnecessary that the nozzle pitch is densified in head 50. The head 50 hasa structure where plural ink chamber units 104 which consist of nozzle100 ejecting the ink droplets and pressure chamber 102 corresponding tothe nozzle 100 is disposed in zigzag in a matrix form, as showed inFIGS. 3 and 4. Thereby, an apparent densified nozzle pitch is attempted.That is to say, the head 50 is a full line head which provides at leastone nozzle row where the plural nozzles 100 ejecting ink are arrangedover the length corresponding to the whole width of the recording mediumin the direction (principal scanning direction) substantially orthogonalto the transfer direction (sub-scanning direction) of the recordingmedium, as shown in FIGS. 3 and 4.

One example of a case where ink is ejected from the nozzle plate havingthe plural nozzles is described in reference to FIG. 5. In FIG. 5, fourrows of nozzle rows from 311 to 341 are shown, but substantially, thetotal of 64 rows are disposed in one head module with a repeatedarrangement pattern in the same manner as the four rows. 32 nozzles arearranged in each nozzle row. In FIG. 5, Y direction is paper transferdirection (sub-scanning direction), and X direction is longitudinaldirection (principal scanning direction) of the line head. When oneprincipal scanning line 260 is ejected, dot 314 is ejected from nozzle312 of nozzle row 311. The dot 324 adjacent to dot 314 in the principalscanning direction is ejected from nozzle 332 of nozzle row 331 in thenext two rows with respect to nozzle row 311. The dot 334 adjacent todot 324 in the principal scanning direction is ejected from nozzle row322 of nozzle row 321 adjacent to nozzle row 311. The dot 344 adjacentto dot 334 in the principal scanning direction is ejected from nozzle342 of nozzle row 341 in the next three rows with respect to nozzle row311. Thus, four nozzle rows are used one by one in the prescribedpattern (nozzle sequence 375 in FIG. 5), and the adjacent dot (forexample, a group of adjacent four dots such as 362 or 364 in FIG. 5) inthe principal scanning direction is ejected.

In FIG. 1, the ink supply unit 20 is equipped with plural pressurechambers 21, which respectively communicate with the plural ejectionopenings (ejection ports) 12 of the nozzle plate 11 through the nozzlecommunication path 22, plural ink supplying paths 23 that respectivelysupply ink to the plural pressure chambers 21, a common liquid chamber25 that supplies ink to the plural ink supplying paths 23, and apressure generation unit 30 that respectively transforms the pluralpressure chambers 21.

The ink supplying paths 23 locate between the ink supply unit 20 and thenozzle plate 11, and an ink which has been supplied to the common liquidchamber 25 is introduced to the ink supplying path 23. One terminal of asupply regulating path 24 which is connected with the pressure chambers21 is connected to the ink supplying path 23 so that an amount of an inksupplied from the ink supplying path 23 to the pressure chamber 21 whichis located adjacent to the pressure generation unit 30 may be regulatedto be a desired one. This system may enable to supply a plenty of amountof ink to the plural ejection openings.

The pressure generation unit 30 is an actuator (piezo device) which isconstituted by sequentially stacking a vibration plate 31, an adhesivelayer 32, a lower electrode 33, a piezoelectric body layer 34, and anupper electrode 35, from the pressure chamber 21 side. The pressuregeneration unit 30 is such that an electrical wire supplying a drivingsignal from the exterior is connected to be driven. The piezoelectricbody layer is joined with electrode on the vibration plate (pressingplate) 31 which constitutes the upper face of pressure chamber 21. Theactuator is deformed according to an image signal by applying anelectric voltage to the electrode. The ink is ejected from the nozzlethrough the nozzle communicating path. When the ink is ejected, new inkis supplied to the pressure chamber 21 through the ink supply path 23from the common liquid chamber 25.

A circulation aperture 41 which continuously collects an ink to acirculation path 42 is provided in the vicinity of the ejection opening12. Increase of viscosity of an ink in the vicinity of the ejectionopening during non-driving period may be suppressed thereby.

FIG. 6 is a perspective diagram showing another preferable example ofthe inner structure of inkjet head. FIG. 7 is a plane perspectivediagram magnifying and showing a part of the pressure chamber. FIG. 8 isa cross-sectional drawing along line 9-9 of FIG. 7.

In order to densify the nozzle pitch, the inkjet head has the nozzleplate 194, plural pressure chambers 152 respectively communicating withthe plural nozzles (ejection port) 151 of the nozzle plate, the pluralink supply flow paths 153 which supply ink to the plural pressurechambers 152, a common liquid chamber 155 which supplies the inkcomposition to each of the plural ink supply flow paths 153, pressuregeneration units 158 which respectively deform the plural pressurechambers 152, and electrical wirings 190 which respectively supplydriving signals to the pressure generation units 158.

In order to obtain a higher precise image, the configuration of theinkjet head, shown in FIGS. 6 to 8, in part or as a whole uses silicon,which is easily used in a semiconductor process, and the rear face flowpath design is used as flow path configuration where large volumes ofink can be ejected with high frequency. Through the rear face flow pathdesign, large volumes of ink can be supplied to the nozzle disposed suchthat a higher precise image can be formed. As a result, fresh inkreadily contacts the nozzle plate at all times. Even though theprotective film is formed on the nozzle plate surface or inside thenozzle plate, silicon erosion in the nozzle plate main body easilyproceeds through contact with ink due to ink penetration at a defectiveportion, or the like of film. In embodiments, through the addition of aninorganic silicate compound to ink composition used in ejection,deterioration of silicon, which is likely to be eroded, can beeffectively prevented.

In the head 150, vibration plate 156, which forms the upper face ofpressure chamber 152, is disposed on the upper side of the pressurechamber 152 having nozzle 151 and ink supply flow path 153. Thepiezoelectric device 158 (piezo actuator) is disposed as the pressuregeneration unit which consists of a piezoelectric body, such as a piezowhich sandwiches an electrode at the upper and lower sides of portioncorresponding to each pressure chamber 152 on vibration plate 156. Thepiezoelectric body 158 has separate electrode 157 on the upper face. Theelectrode pad 159 is drawn and formed as an electrode connecting sectionfrom the edge face of the separate electrode 157 to outside. Theelectrical wiring 190 on the electrode pad 159 is stood substantiallyvertically to the face including the piezoelectric device 158 (pressuregeneration unit). The multilayer flexible cable 192 is disposed on theelectrical wiring 190 which is stood substantially vertically withrespect to the face including the piezoelectric device 158, and thedriving signal is supplied through the wiring from head driver to theseparate electrode 157 of the piezoelectric device 158.

The space of the columnar electrical wiring (electrical column) 190,between where the vibration plate 156 and the flexible cable 192 arealigned, is a common liquid chamber 155 for supplying ink to pressuregenerating chamber 152 through the ink supply flow path 153 from hereto.

The electrical wiring 190 which is stood as a vertical column on theelectrode pad 159 drawn from the separate electrode 157 to pressurechamber 152 supports the flexible cable 192 from below, and the space ofthe common liquid chamber 155 is formed. The electrical wiring 190 isformed to penetrate the common liquid chamber 155. Further, theelectrical wiring 190 is formed with respect to the piezoelectric device158 (of the separate electrode 157) one by one and is corresponded toone-on-one. However, in order to decrease number of wirings (electricalcolumn number), one electrical wiring 190 may correspond to pluralpiezoelectric devices 158 such that the wirings for some piezoelectricdevices 158 collectively form one electrical wiring 190. Further, wiringfor not only separate electrodes 157 but a common electrode (vibratingplate 156) may be formed as the electrical wiring 190.

As shown in FIG. 6, the nozzle 151 is formed on the bottom face, and theink supply flow path 153 is provided at the upper face of the diagonalcorner to the nozzle 151. The ink supply flow path 153 penetrates thevibrating plate 156 and the common liquid chamber 155 and the pressurechamber 152 thereon is directly connected through the ink supply flowpath 153. Thereby, the common liquid chamber 155 and the pressurechamber 152 can be directly fluidically connected.

The vibrating plate 156 is common to each pressure chamber 152 and formsone plate. The piezoelectric device 158 for deforming the pressurechamber 152 is disposed in the portion corresponding to the pressurechamber 152 of the vibrating plate 156. The electrode (common electrodeand separate electrode) for driving the device by applying the electricvoltage to the piezoelectric device 158 is formed at the upper and lowerfaces so as to sandwich the piezoelectric device 158.

The vibrating plate 156 may be formed of a conductive thin film such as,for example SUS, or the like to serve as a common electrode. In thiscase, in order that the piezoelectric device 158 is individually driven,a separate electrode 157 is formed in the upper face of piezoelectricdevice 158.

As described above, the electrode pad 159 is drawn from the separateelectrode 157, and the electrical wiring 190 (electric column) whichstands vertically on the electrode pad 159, and penetrates the commonliquid chamber 155 is formed. In the electrical wiring 190 (electriccolumn), the electrical wiring 190 is formed in a tapered shape duringthe production process as shown in FIG. 7.

The multilayer flexible cable 192 is formed on columnar electricalwiring 190. The electrical wiring 190 is a column to support themultilayer flexible cable 192, the vibrating plate 156 is used as thefloor, the multilayer flexible cable 192 is used as the ceiling, and thespace for the common liquid chamber 155 is secured. Further, theelectrical wirings 190 are respectively connected to separate wirings(not shown) to supply driving signals to each electrodes 157, andthereby piezoelectric devices 158 are driven.

FIG. 7 shows a plane perspective diagram magnifying a part of thepressure chamber 152. As described above, the pressure chamber 152 issubstantially square in shape, and the nozzle 151 and the ink supplyflow path 153 are formed at diagonally opposed corners to each other,the electrode pads 159 is drawn to the nozzle 151 side, and theelectrical wirings (electrical column) 190 are formed thereon.

As shown in FIG. 8, the head 150 is formed by laminating plural thinfilms, or the like.

The flow path plate 196 is laminated where the nozzle flow path 151 a orthe like, which connects the pressure chamber 152, the ink supply port153 and the pressure chamber 152 with the nozzle 151, is formed on thenozzle plate 194 forming the nozzle 151. Here, the flow path plate 196is represented as one plate although, in practice, the flow path plate196 may be formed by laminating plural plates.

Further, a part or the whole of the nozzle plate 194 is formed ofsilicon. A structure may be used where the silicon is exposed within thenozzle port and on a surface thereof at a side toward the ink ejectiondirection of the nozzle, which are preferably coated with a film whichcontains at least one kind selected from the group consisting of metal(including silicon) oxide, metal nitride, and metal (excluding silicon).Among them, the nozzle plate is most preferably provided with SiO₂ filmformed by a method of chemical vapor deposition (CVD), in at least apart thereof or entirely.

Further, the surface thereof at a side toward the ink ejection directionof the nozzle plate may be coated with a liquid repellent film in orderthat wettability due to ink is suppressed to prevent ink stain in thevicinity of nozzle. As the liquid repellent film, a film includingfluorocarbon is preferably used.

Further, in exemplary embodiments of the invention, a deposited filmincluding a fluoroalkylsilane moiety is formed by the chemical vapordeposition (CVD) method using C₈F₁₇C₂H₄SiCl₃ on SiO₂ film.

The vibration plate 156 forming the upper face of the pressure chamber152 is laminated on the flow path plate 196. The vibration plate 156preferably serves as a common electrode for driving the piezoelectricdevice 158 together with the separate electrode 157. Further, an openingcorresponding to ink supply flow path 153 of the pressure chamber 152 isprovided in the vibrating plate 156, to thereby directly communicate thecommon liquid chamber 155 formed on the vibrating plate 156 with thepressure chamber 152.

The piezoelectric body 158 a is formed in the portion corresponding tosubstantially the entire face of the upper face of the pressure chamber152 on the vibrating plate 156 (common electrode) and the separateelectrode 157 is formed in the upper face of the piezoelectric body 158a.

The piezoelectric body 158 a, which is interposed between the commonelectrode (vibrating plate 156) and separate electrode 157 on the upperand lower side, modifies the pressure chamber 152 to reduce the volumethereof when an electric voltage is applied by the common electrode 156and the separate electrode 157, and constitutes a piezoelectric device158 (piezoelectric actuator) for ejecting ink from the nozzle 151.

The edge of the nozzle 151 of the separate electrode 157 forms theelectrode pad 159 as the electrode connecting section which is drawnoutward. The columnar electrical wiring 190 (electric column) is formedvertically on the electrode pad 159 so as to penetrate the common liquidchamber 155.

The multilayer flexible cable 192 is formed on the electrical wiring190. Each wiring (not shown) formed in the multilayer flexible cable 192connects the electrode pad 190 a to the electrical wiring 190, a drivingsignal is supplied through the electrical wiring 190 in order to driveeach piezoelectric device 158.

The space where the columnar electrical wiring 190 (electric column)between the vibration plate 156 and the multilayer flexible cable 192 isaligned is the common liquid chamber 155 filled with ink in order tosupply ink to the pressure chamber 152 which pools ink. Here, in orderto fill the ink, insulation and protective films 198 are formed on theink contacting surfaces of the vibrating plate 156, the separateelectrode 157, the piezoelectric body 158 a, and the electrical wiring190, as well as the multilayer flexible cable 192.

The common liquid chamber which has been conventionally on the same sideas the pressure chamber with respect to the vibration plate is disposedhere on the vibration plate and is provided in opposition to thepressure chamber. Therefore, the conventionally required pipe, or thelike for introducing ink to the pressure chamber from the common liquidchamber is not necessary. Further, the size of the common liquid chambercan be increased, and thereby ink can be satisfactorily supplied anddensification of the nozzles can be attained. With the achievement ofdensification, the nozzles can be driven at a high frequency. Wiring tothe separate electrode of each piezoelectric device is stood verticallyfrom the electrode pad of the separate electrode, and is made topenetrate the common liquid chamber. Therefore, the wiring for supplyinga driving signal to each piezoelectric device can be densified. Further,the common liquid chamber is disposed on the vibrating plate, the commonliquid chamber and pressure chamber is directly connected through theink supply port. Thereby, the common liquid chamber and pressure chambercan be directly fluidically connected, and the common liquid chamber isdisposed on the vibrating plate. Therefore, the length of the nozzleflow path 151 a from the pressure chamber 152 to nozzle 151 can beshortened over conventional methods. Even in the case of densification,high viscosity ink (for example, about 20 cp to 50 cp) can be ejected.Further, a flow path structure can be made which is able to promptlyrefill after ejection.

Further, the inner structure of inkjet head, shown in FIGS. 6 to 8 isdescribed in [0090] to [0113] of JP-A No. 2006-111000.

[Treatment Liquid Applying Step]

In an image forming method of the exemplary embodiment of the invention,a treatment liquid applying step may be provided, which performs imagingby applying a treatment liquid configured to form aggregates whencontacted with the ink composition, to a recording medium, and placingthe treatment liquid in contact with an ink composition. In this case,dispersed particles of the polymer particles or coloring material (forexample, pigment) in the ink composition aggregate, and an image isfixed to the recording medium. In addition, the details and preferredembodiments of the respective components in the treatment liquid are asdescribed previously.

Application of the treatment liquid may be performed by applying knownmethods such as a coating method, an inkjet method, and an immersionmethod. The coating method may be performed by a known coating methodusing a bar coater, an extrusion die coater, an air doctor coater, abread coater, a rod coater, a knife coater, a squeeze coater, or areverse roll coater. Details of the inkjet method are as describedabove.

The treatment liquid discharging step may be provided before or afterthe ink applying step using the ink composition.

In embodiments, an embodiment in which the ink discharging step isprovided after the treatment liquid is applied in a treatment liquidapplying step, is preferable. That is, an embodiment in which, beforeapplication of the ink composition on the recording medium, a treatmentliquid for aggregating a coloring material (preferably pigment) in theink composition is applied in advance, and the ink composition isapplied so as to contact the treatment liquid applied on the recordingmedium to form an image, is preferable. Thereby, inkjet recording may bespeeded-up and, even when high speed recording is performed, an imagehaving high density, and high resolution is obtained.

The amount of application of the treatment liquid is not particularlylimited so long as the liquid can aggregate the ink composition, but canbe an amount resulting in an amount of application of the aggregatedcomponent (for example, a carboxylic acid or a cationic organic compoundhaving a valency of 2 or greater) of 0.1 g/m² or more. Among them, anamount resulting in an amount of application of the aggregated componentof 0.1 to 1.0 g/m² is preferred, and an amount resulting in 0.2 to 0.8g/m² is more preferred. When the amount of application of the aggregatedcomponent is 0.1 g/m² or more, the aggregation reaction proceedssatisfactorily, and when the amount is 1.0 g/m² or less, the glossinessis not very high, and is preferable.

According to the exemplary embodiment of the invention, it is preferableto provide an ink discharging step after the treatment liquid applyingstep, and to further provide a heating drying step of heating and dryingthe treatment liquid on the recording medium, during a period from afterapplying the treatment liquid onto the recording medium until the inkcomposition is applied. By heating and drying the treatment liquidpreviously before the ink discharging step, ink coloring properties suchas the prevention of spreading becomes good, and a visible image havinggood color density and hue can be recorded.

The heating and drying can be carried out by a known heating means suchas heater, an air blowing means utilizing air blowing such as dryer, ora means combining these. Examples of the heating method include a methodof supplying heat by a heater or the like, from the surface of therecording medium opposite the surface applied with the treatment liquid,a method of blowing a warm air or hot air to the surface of therecording medium applied with the treatment liquid, a method of heatingusing an infrared heater, or the like. Heating can also be performed bycombining these methods.

[Heating Fixing Step]

It is preferable that the image forming method of the exemplaryembodiment of the invention includes, after the ink applying step, aheating fixing step for heating and fixing the ink image formed by theapplication of the ink composition by placing the image in contact witha heated surface. By adding a heating fixing treatment, fixing of theimage on the recording medium is achieved, and the resistance of theimage to abrasion can be further enhanced.

Heating can be preferably performed at the glass transition temperature(Tg) or higher of the polymer particle in the image. Since heating isperformed at the Tg temperature or higher, the film is formed tostrengthen the image. The heating temperature is preferably in thetemperature region of Tg+10° C. or higher. Specifically, the heatingtemperature is preferably in a range of from 40° C. to 150° C., morepreferably in a range of from 50° C. to 100° C., and even morepreferably in a range of from 60° C. to 90° C.

From the viewpoint of surface smoothing, a pressure duringpressurization together with heating is preferably in a range of from0.1 MPa to 3.0 MPa, more preferably in a range of from 0.1 MPa to 1.0MPa, and even more preferably in a range of 0.1 MPa to 0.5 MPa.

The heating method is not particularly limited, but methods ofnon-contact drying such as a method of heating with a heat generatorsuch as a nichrome wire heater; a method of supplying warm air or hotair; and a method of heating with a halogen lamp, an infrared lamp orthe like, may be suitably exemplified. The method of heating andpressing is not particularly limited, but methods of performing heatingand fixing by contact such as, for example, a method of pressing a heatplate to the image-formed surface of the recording medium, and a methodof passing the image through a pair of rollers using a heating andpressing apparatus equipped with a pair of heating and pressing rollers,a pair of heating and pressing belts, or a heating and pressing beltdisposed on the side of the image-recorded surface of the recordingmedium and a retaining roller disposed on the opposite side, may besuitably mentioned.

In the case of heat and pressing, a NIP time of 1 msec to 10 sec ispreferable, more preferable is 2 ms to 1 s, and even more preferable is4 msec to 100 msec. Further, a NIP width of 0.1 mm to 100 mm ispreferable, more preferable is 0.5 mm to 50 mm, and even more preferableis 1 mm to 10 mm.

As the heating and pressing roller, a metal roller made from metal or aroller having a coating layer including an elastic body around a metalbar core and a surface layer (referred to as separate layer) provided ifnecessary, may be used. For example, the latter bar core can beconstituted by a cylindrical body made from iron, aluminum, SUS, or thelike. The surface of the bar core is preferably coated with the coatinglayer at least in part. In particular, the coating layer may bepreferably formed of a silicon resin or fluorocarbon resin having moldreleasability. Further, a heat generation unit is preferably built intothe bar core of one side of the heating and pressing roller, and heatingand pressing process are simultaneously preformed by passing therecording medium between rollers or heating may be performed throughsandwiching the recording medium using two heating rollers, ifnecessary. For example, the heat generation unit is preferably a halogenlamp heater, a ceramic heater, a nichrome wire, or the like.

A belt base material which constitutes a heating and pressing belt usedin the heating and pressing unit is preferably a seamless electroformednickel, the thickness of the base material is preferably 10 to 100 μm.Further, aluminum, iron, polyethylene, or the like, other than nickelcan be used as the material of belt base material. When silicon resin orfluorocarbon resin is provided, the thickness of layer which is formedby using the resins is preferably 1 to 50 μm, and more preferably 10 to30 μm.

Further, in order to realize the pressure (NIP pressure), elasticmembers such as springs with tensile force are selected and are disposedin both ends of rollers such as a heating and pressing roller so as toobtain the desired NIP pressure in consideration of the NIP gap.

The speed of conveyance of the recording medium when a heating andpressing roller or a heating and pressing belt is used is preferably inthe range of 200 mm/second to 700 mm/second, more preferably 300mm/second to 650 mm/second, and further preferably 400 mm/second to 600mm/second.

—Recording Medium—

The image forming method of the exemplary embodiment of the invention isto record an image on the recording medium.

The recording medium is not particularly limited, and general printingpaper including cellulose as a main component such as so-calledhigh-quality paper, coated paper, and art paper may be used. The generalprinting paper including cellulose as a main component absorbs and driesan ink relatively slowly, easily causes coloring material movement aftera droplet is spotted, and allows image quality to easily deteriorate inimage recording by a general inkjet method using an aqueous ink.However, according to the image forming method of the exemplaryembodiment of the invention, coloring material movement is suppressed,and a high-quality image excellent in color density and hue may berecorded.

As the recording medium, a recording medium which is generallycommercially available may be used, and examples include high qualitypaper such as OK Prince High Quality (trade name, manufactured by OjiPaper Co., Ltd.), Shiorai (trade name, manufactured by Nippon PaperIndustries Co., Ltd.), and New NP High Quality (trade name, manufacturedby Nippon Paper Industries Co., Ltd.), fine coated paper such as OK EverLite Coat (trade name, manufactured by Oji Paper Co., Ltd.) and Aurora S(trade name, Nippon Paper Industries Co., Ltd.), light coated paper (A3)such as OK Coat L (trade name, manufactured by Oji Paper Co., Ltd.) andAurora L (trade name, manufactured by Nippon Paper Industries Co.,Ltd.), coated paper (A2, B2) such as OK Top Coat+ (trade name,manufactured by Oji Paper Co., Ltd.) and Aurora Coat (trade name,manufactured by Nippon Paper Industries Co., Ltd.), and an art paper(A1) such as OK Kanefuji+ (trade name, manufactured by Oji Paper Co.,Ltd.) and Tokubishi Art (trade name, manufactured by Nippon PaperIndustries Co., Ltd.). Further, various papers for photography for usein inkjet recording may be used.

Among the above, a recording medium having a water-absorptioncoefficient Ka of 0.05 mL/m²·ms^(1/2) to 0.5 mL/m²·ms^(1/2) ispreferable, a recording medium having a water-absorption coefficient Kaof 0.1 mL/m²·ms^(1/2) to 0.4 mL/m²·ms^(1/2) is more preferable, and arecording medium having a water-absorption coefficient Ka of 0.2mL/m²·ms^(1/2) to 0.3 mL/m²·ms^(1/2) is even more preferable from theviewpoints of the large suppression effect on color material movementand obtaining high quality image having good color density and color huecompared to conventional methods.

The water-absorption coefficient Ka has the same definition as thatdescribed in JAPAN·TAPPI·Paper Pulp Testing Method No 51:2000 (publishedby Japan Technical Association of the Pulp and Paper Industry).Specifically, the absorption coefficient Ka is calculated fromdifference of the transferring amount of water in contact time 100 msand 900 ms by using Automatic Scanning Absorptometer KM500Win (tradename, manufactured by Kumagai Riki Kogyo Co., Ltd.).

Among recording mediums, there is preferred a so-called coated paperused in general offset printing, or the like. The coated paper is acoating layer provided by applying a coating material on the surface ofa high-quality paper, a neutralized paper, or the like which mainly usecellulose and are generally not surface-treated. The coated paper easilycauses problems in quality in gloss or abrasion resistance of the image,or the like in forming an image by a conventional water-based inkjetmethod. In the image forming method of the exemplary embodiment of theinvention, gloss unevenness can be suppressed to obtain good imagehaving glossy and abrasion resistance. In particular, the coated paperis preferably used which has base paper and a coating layer includingkaolin and/or calcium bicarbonate. More specifically, an art paper, acoated paper, a lightweight coated paper or a micro coated paper aremore preferred.

—Ink Composition—

The ink composition of the exemplary embodiment of the inventionincludes an inorganic silicate compound and is generally composed byincluding a further colorant such as a pigment or dye, and further, iscomposed by using another component if necessary. In embodiments, thecomposition which contains pigments and an inorganic silicate compoundis preferable. The pigment (hereinafter, referred to as “resin-coatedpigment”) is coated with a water insoluble resin including a structuralunit having an acidic group.

By using an ink composition constituted by including an inorganicsilicate compound and preferably a resin-coated pigment, deteriorationby erosion of the nozzle plate of the inkjet head is suppressed and isexcellent in the ejection reliability of ink. Further, the abrasionresistance of the formed image is increased.

The liquid repellent film is provided to a member constituting theinkjet head to give the liquid repellent property in order to maintainthe ejection performance of the ink. For example, the liquid repellentproperty can be given to the surface of the head member, preferably thesilicon surface by a surface treatment using the fluorine material. Itis known that the liquid repellent property of the inkjet head member isdeteriorated slowly due to long-term use of the inkjet head.

Meanwhile, in particular, in order that a fine nozzle (ink ejectionport) is formed precisely, the nozzle plate is formed by containingsilicon in some cases. In the inkjet head having the silicon nozzleplate formed by the use of silicon, even though a fluorocarbon film aswell as a liquid repellent film are provided at the surface thereof,deterioration of the liquid repellent property or deterioration of theliquid repellent property of the nozzle plate due to ink penetrationthrough a pinhole generated in the film, or deformation of the silicondue to ink penetration through a pinhole, or the like has an effect onthe ink ejection property in some cases.

When the ink composition of the exemplary embodiment of the invention isused in an inkjet head having such (preferably formed of silicon) anozzle plate, deterioration of the liquid repellent property of the headmember and further deterioration of the silicon under the liquidrepellent film can be prevented effectively.

The ink composition of the exemplary embodiment of the inventioncontains at least one kind of an inorganic silicate compound. Theinorganic silicate compound may be widely selected from silicic acid andsilicate; in particular, salt with alkali metal and alkali earth metalof silicic acid such as sodium silicate, potassium silicate, calciumsilicate, and magnesium silicate, or anhydrous silicic acid (silica) ispreferable. An alkali solution of an alkali metal salt of silicic acidwhich is referred to as water glass is preferably used as the silicate.The anhydrous silicic acid (silica) is not particularly limited, butcolloidal silica is preferably used.

As far as the alkali metal salt of silicic acid is a compound which isconstituted by silicon dioxide and metallic oxide and has watersolubility, it is not particularly limited. The alkali metal salt ofsilicic acid includes alkali metal salt of metasilicic acid, alkalimetal salt of orthosilicic acid, or the like. Further, an ammonium saltof silicic acid including an ammonium salt of metasilicic acid, ammoniumsalt of orthosilicic acid, or the like may be also used. The silicatesalt having water solubility may be used alone or in a combination withtwo or more kinds thereof.

Specifically, the alkali metal salt of silicic acid is preferably atleast one kind of compound represented by the following formula (S).x(M₂O)·y(SiO₂)  Formula (S)

In Formula (S), M represents sodium or potassium, x represents 1 or 2, yrepresents an integer of 1 to 4. The alkali metal salt of silicic acidrepresented by Formula (S) is referred as the alkali metal salt ofsilicic acid when x=1, y=1, alkali metal salt of orthosilicic acid whenx=2, y=1, and both are alkali metal salt of silicic acid having watersolubility.

As the alkali metal salt of silicic acid having water solubility, acommercial compound (for example, water glass), or one obtained bysolving silicic acid and carbonate or hydroxide of alkali metal may beused.

Among them, from the viewpoints of suppressing elution of the portioncontacting the ink composition of the inkjet head (particularly, nozzleplate or ink flow path), and an erosion according to the elution,incorporating at least one kind selected from alkali metal salt ofsilicic acid such as sodium silicate and potassium silicate in the inkcomposition is preferable. The alkali metal salt of silicic acid rendersto obtain good ink dispersibility to the ink composition in comparisonwith salt other than alkali metal, for example ammonium salt of silicicacid (for example, tetramethyl ammonium salt of silicic acid, or thelike). Further, in the case of ammonium salt, or the like, a volatilecompound can be produced in some cases, and thus an alkali metal salt ofsilicic acid is preferable from the viewpoint that over time odors arehardly generated.

Colloidal silica is colloid that comprises fine particles of inorganicoxides including silicon, in which an average particle diameter of thefine particles is several hundred nm or less. Colloidal silica includessilicon dioxide (including hydrates thereof) as a main component and maycontain aluminate as a minor component. Examples of the aluminate, whichmay be contained as a minor component, include sodium aluminate andpotassium aluminate.

Further, inorganic salts such as sodium hydroxide, potassium hydroxide,lithium hydroxide, and ammonium hydroxide or organic salts such astetramethylammonium hydroxide may be contained in the colloidal silica.These inorganic salts and organic salts function, for example, as astabilizer of colloid.

The dispersing medium for colloidal silica is not particularly limitedand may be any of water, an organic solvent, or a mixture of water andan organic solvent. The organic solvent may be a water-soluble organicsolvent or a water-insoluble organic solvent. However, the organicsolvent is preferably a water-soluble organic solvent. Specific examplesthereof include methanol, ethanol, isopropyl alcohol, and n-propanol.

There is no particular limitation on the method for producing colloidalsilica, and colloidal silica can be produced by a generally used method.For example, colloidal silica can be produced through an Aerosilsynthesis by thermal decomposition of silicon tetrachloride, or may beproduced from water glass. Alternatively, colloidal silica can beproduced according to a liquid phase synthesis method includinghydrolysis of an alkoxide (see, for example, “Seni to Kogyo”, vol. 60,No. 7, page 376, 2004), or the like.

There is no particular limitation on the average particle diameter ofthe particles contained in the colloidal silica according to the presentinvention. For example, the average particle diameter may be set from 1nm to 200 nm. The average particle diameter is preferably from 1 nm to100 nm, more preferably from 3 nm to 50 nm, even more preferably from 3nm to 25 nm, and particularly preferably from 5 nm to 20 nm.

When the average particle diameter is 200 nm or less, damages (forexample, lowering of liquid repellency or the like) caused by ink to themembers which construct the inkjet head, such as a substrate, aprotective film, a liquid-repellent film, and the like, may be moreeffectively suppressed. It is thought that, by making the averageparticle diameter smaller, a total surface area of particles increases,so that damages to the members which construct the inkjet head is moreeffectively suppressed. Moreover, it is preferable that the averageparticle diameter of the particles is 200 nm or less, also from theviewpoints of discharge reliability of the ink composition andsuppression of the abrasive effect caused by the particles.

In the present invention, the average particle diameter of the colloidalsilica is represented by a volume average particle diameter. The volumeaverage particle diameter can be determined according to a generalmethod for dispersed particles such as a light scattering method or alaser diffraction method.

The shape of the colloidal silica is not particularly limited so long asit does not disturb the ejection performance of the ink. For example,the shape may be a spherical shape, a long shape, a needle-like shape,or a shape like a string of beads. Above all, it is preferred that thecolloidal silica is spherical, from the viewpoint of dischargeability ofink.

The colloidal silica, which can be used in the present invention, may beproduced by the production method described above, or may be acommercially available product. Specific examples of the commerciallyavailable product include LUDOX AM, LUDOX AS, LUDOX LS, LUDOX TM, andLUDOX HS (all trade names, manufactured by E.I. Du Pont de Nemours &Co.); SNOWTEX S, SNOWTEX XS, SNOWTEX 20, SNOWTEX 30, SNOWTEX 40, SNOWTEXN, SNOWTEX C, and SNOWTEX O (all trade names, manufactured by NissanChemical Industries, Ltd.); SYTON C-30 and SYTON ZOO (all trade names,manufactured by Monsanto Co.); NALCOAG-1060 and NALCOAG-ID21 to 64 (alltrade names, manufactured by Nalco Chem. Co.); METHANOL SOL, IPA SOL,MEK SOL, and TOLUENE SOL (all trade names, manufactured by Fuso ChemicalCo., Ltd.), CATALOID-S, CATALOID-F120, CATALOID SI-350, CATALOID SI-500,CATALOID SI-30, CATALOID S-20L, CATALOID S-20H, CATALOID S-30L, CATALOIDS-30H, CATALOID SI-40, and OSCAL-1432 (isopropyl alcohol sol) (all tradenames, manufactured by JGC Catalysts and Chemicals Ltd.); ADELITE (tradename, manufactured by Asahidenka Co., Ltd.); and, as examples ofcolloidal silica in the shape of a string of beads, SNOWTEX ST-UP,SNOWTEX PS-S, SNOWTEX PS-M, SNOWTEX ST-OUP, SNOWTEX PS-SO, and SNOWTEXPS-MO (all trade names, manufactured by Nissan Chemical Industries,Ltd.). These products are easily available.

The pH of the above commercially available colloidal silica dispersionliquid is often adjusted to pH of acidic or alkaline. This is becausethe region where colloidal silica is stably dispersed exists in anacidic side or alkaline side. In the case of adding a commerciallyavailable colloidal silica dispersion liquid to the ink composition, thepH of the region where the colloidal silica is stably dispersed and thepH of the ink composition should be taken in consideration.

The content of the colloidal silica in the ink composition, while notparticularly limited, can be for example 0.0005% by mass to 0.5% by masswith respect to the total amount (entire mass) of the ink composition.The content of the inorganic silicate compound is preferably 0.001% bymass to 0.5% by mass with respect to the total amount of the inkcomposition, more preferred is 0.01% by mass to 0.5% by mass of thetotal amount of the ink composition, and particularly preferred is 0.01%by mass to 0.3% by mass of the total amount of the ink composition. Whenthe content of the ink composition is the upper limit or less, theejection properties of the ink composition is more improved, furtherinfluence on inkjet head due to abrasive effect of silica particle canbe suppressed more effectively. Further, when the content of the inkcomposition is the lower limit or higher, shape deformation bydeterioration due to erosion of the nozzle plate and decrease in liquidrepellent property can be suppressed more effectively.

Further, in the ink composition of the exemplary embodiment of theinvention, it is preferable that the content of colloidal silica whichhas volume average particle diameter of 3 nm to 25 nm is 0.001% by massto 0.5% by mass with respect to the total amount of the ink composition,from the viewpoints of suppression of the decrease in liquid repellentproperty of the inkjet head member and the ink ejection properties. Itis more preferred that the content of colloidal silica which has volumeaverage particle diameter of 3 nm to 20 nm is 0.01% by mass to 0.5% bymass of the total amount of the ink composition.

[Colorant]

The ink composition of the exemplary embodiment of the invention cancontain color elements such as pigments or dyes as colorants. Inembodiments, it is preferred to contain at least one kind of pigmentwhich is coated with a water-insoluble resin including a structural unithaving an acidic group. Thereby, the ink composition of the exemplaryembodiment of the invention is excellent in ink ejection reliability andis excellent in abrasion resistance of the formed image therewith. Inthis case, a specific form of pigment is not particularly limited, aslong as there is a form where the whole or a part of the surface of thepigment particles is coated with the water insoluble resin.

<Pigment>

The pigment used in the exemplary embodiment of the invention is notparticularly limited, and may be appropriately selected according to theintended use. The pigment includes an organic pigment and an inorganicpigment.

Examples of the organic pigment include azo pigments, polycyclicpigments, dye chelates, nitro pigments, nitroso pigments, and anilineblack. Among them, azo pigments and polycyclic pigments are morepreferable.

Examples of the azo pigments include azo lakes, insoluble azo pigments,condensed azo pigments, and chelate azo pigments.

Examples of the polycyclic pigment include phthalocyanine pigments,perylene pigments, perinone pigments, anthraquinone pigments,quinacridone pigments, dioxazine pigments, indigo pigments, thioindigopigments, isoindolinone pigments, and quinophthalone pigments.

Examples of the dye chelates include basic dye chelates and acidic dyechelates.

Examples of the inorganic pigments include titanium oxide, iron oxide,calcium carbonate, barium sulfate, aluminium hydroxide, barium yellow,cadmium red, chrome yellow, and carbon black. Among them, carbon blackis particularly preferable. Carbon black may be produced by a knownmethod such as a contact method, a furnace method, or a thermal method.

These pigments may be used alone or in a combination of two or more ofthem selected from one or more groups above.

(Water-Insoluble Resin)

The water-insoluble resin contains at least one structural unit havingan acidic group, and may further contain one or more other structuralunit(s) if necessary. In preferable embodiments, in view of achievingstable presence in the ink composition, reducing adhering andaccumulation of aggregates, and enabling easy removal of adheredaggregates, the water-insoluble resin may preferably contain at leastone hydrophilic structural unit (A) and at least one hydrophobicstructural unit (B). In more preferable embodiments, the acidic groupmay be contained in one of the hydrophilic structural unit (A).

The “water-insoluble polymer” herein refers to a polymer whose dissolvedamount to 100 g of water at 25° C. is 5 g or smaller when the polymer isdissolved in the water. The “dissolved amount” is an amount of (a partof) the water-insoluble polymer dissolved in a solvent (water) whenacidic groups of the water-insoluble polymer are completely neutralizedwith sodium hydroxide.

Hydrophilic Structural Unit

There is no particular limitation to the hydrophilic structural unit inthe water-insoluble polymer as long as it contains at least onehydrophilic functional group. The hydrophilic structural unit maycontain an ionic hydrophilic group or a nonionic hydrophilic group. Inpreferable embodiments, the hydrophilic structural unit may have anacidic group. The hydrophilic structural unit having an acidic group maybe derived from a monomer including an acidic group, or may be astructural unit formed by introducing, by a macromolecular reaction, anacidic group to a structural unit having no acidic group in a polymerchain which has been formed by polymerization.

The acid group is not particularly limited and may include, from theviewpoint of stability of the emulsion state or dispersion state, acarboxy group, a phosphoric acid group, and a sulfonic acid group. Amongthese, a carboxy group is preferable from the viewpoint of dispersionstability in an ink composition.

As a monomer having an acid group (acid group containing monomer), amonomer having an acid group and an ethylenically unsaturated bond ispreferable. Examples of the monomer having an acid group may include anunsaturated carboxylic acid monomer, an unsaturated sulfonic acidmonomer, and an unsaturated phosphoric acid monomer.

Examples of the unsaturated carboxylic monomer may include acrylic acid,methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaricacid, citraconic acid, and 2-methacryloyloxymethyl succinic acid.Examples of the unsaturated sulfonic acid monomer may includestyrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid,3-sulfopropyl (meth)acrylate, and bis(3-sulfopropyl) itaconate. Examplesof the unsaturated phosphoric acid monomer may include vinylphosphonicacid, vinyl phosphate, bis(methacryloxyethyl) phosphate,diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethylphosphate, and dibutyl-2-acryloyloxyethyl phosphate.

Among the acid group containing monomers, from the viewpoints ofdispersion stability and ejection stability, an unsaturated carboxylicmonomer is preferable, and acrylic acid and methacrylic acid are morepreferable. Specifically, the structural unit having an acid group ispreferably a structural unit derived from (meth)acrylic acid.

In the water-insoluble resin, either or both of a structural unitderived from acrylic acid and a structural unit derived from methacrylicacid are preferably incorporated.

When the hydrophilic group includes a basic group, examples of the basicgroup include an amino group and an amido group in which a nitrogen atomis unsubstituted.

Examples of the hydrophilic structural unit (A) having a basic groupinclude a structural unit derived from a monomer having a basichydrophilic group. Examples of the monomer having a basic hydrophilicgroup include (meth)acrylate having a basic hydrophilic group,(meth)acrylamide having a basic hydrophilic group, and vinyl monomerssuch as vinyl esters having a basic hydrophilic group.

A monomer which provides the hydrophilic structural unit having a basichydrophilic group may preferably have a functional group which can forma polymer such as an ethylenically unsaturated bond and a basichydrophilic functional group. Such monomer may be selected from knownmonomers, and specific examples thereof which may be preferably usedinclude (meth)acrylamides, aminoethyl (meth)acrylates, and aminopropyl(meth)acrylates.

When the hydrophilic group includes a nonionic hydrophilic group,examples of the nonionic hydrophilic group include a hydroxyl group andalkylene oxides such as polyethylene oxide or polypropylene oxidedescribed below.

Examples of the hydrophilic structural unit (A) having a nonionichydrophilic group include a unit derived from a monomer having anonionic hydrophilic group. Examples of the monomer having a nonionichydrophilic group include (meth)acrylate having a nonionic hydrophilicgroup, (meth)acrylamide having a nonionic hydrophilic group, and vinylmonomers such as vinyl esters having a hydrophilic group.

The monomer that forms the hydrophilic structural unit having a nonionichydrophilic group is preferably a monomer that has a functional groupcapable of forming a polymer such as an ethylenically unsaturated bondand a nonionic hydrophilic functional group, and may be selected fromknown monomers. Preferable specific examples of the monomer may includehydroxylethyl (meth)acrylate, hydroxybutyl (meth)acrylate, and(meth)acrylate that contains an alkyleneoxide polymer.

The hydrophilic structural unit (A) having a nonionic hydrophilic groupmay be formed by polymerization of corresponding monomers, but may beformed by introducing a hydrophilic functional group into a polymerchain after polymerization.

As the hydrophilic structural unit having a nonionic hydrophilic group,a hydrophilic structural unit having an alkylene oxide structure is morepreferable. As the alkylene moiety of the alkylene oxide structure, fromthe viewpoint of hydrophilicity, an alkylene moiety having 1 to 6 carbonatoms is preferable, an alkylene moiety having 2 to 6 carbon atoms ismore preferable, and an alkylene moiety having 2 to 4 carbon atoms isparticularly preferable. The polymerization degree of the alkylene oxidestructure is preferably 1 to 120, more preferably 1 to 60, andparticularly preferably 1 to 30.

In a preferable embodiment, the hydrophilic structural unit having anonionic hydrophilic group is a hydrophilic structural unit havinghydroxy group. The number of hydroxy groups in the structural unit isnot particularly limited and is preferably 1 to 4, more preferably 1 to3, and still more preferably 1 or 2, from the viewpoints of thehydrophilicity of the water-insoluble resin and compatibility with asolvent and other monomers at the time of polymerization.

In the foregoing description, the content of the hydrophilic structuralunit varies, for example, depending on the ratio of the hydrophobicstructural unit (B) described later. For example, when thewater-insoluble resin is composed of acrylic acid and/or methacrylicacid (hydrophilic structural unit (A)) and the hydrophobic structuralunit (B) described later, the content of acrylic acid and/or methacrylicacid is determined by “100−(% by mass of the hydrophobic structuralunit)”.

The hydrophilic structural units (A) may be used alone or as a mixtureof two or more of them.

—Hydrophobic Structural Unit—

In embodiments, the water-insoluble polymer may preferably further haveat least one hydrophobic structural unit (B) other than the structuralunit having an acidic group. There is no particular limitation to thehydrophobic structural unit in the water-insoluble polymer as long as itcontains at least one hydrophobic functional group. In embodiments, thehydrophobic structural unit may preferably include at least onestructural unit having an aromatic ring, and may more preferably includea structural unit represented by the following Formula (1).

In Formula (1), R₁ represents a hydrogen atom or a methyl group. L₁represents an unsubstituted or substituted phenylene group. L₂represents a single bond or a divalent linking group. Ar¹ represents amonovalent group derived from a condensed aromatic ring having 8 or morecarbon atoms, a heterocycle having an aromatic ring condensed therein,or a compound having two or more benzene rings linked to each other.

In Formula (1), R₁ represents a hydrogen atom or a methyl group, andpreferably a methyl group.

L₁ represents an unsubstituted or substituted phenylene group. Anunsubstituted phenylene group is preferable as L₁. L₂ represents asingle bond or a divalent linking group. The divalent linking group ispreferably a linking group having 1 to 30 carbon atoms, more preferablya linking group having 1 to 25 carbon atoms, even more preferably alinking group having 1 to 20 carbon atoms, and particularly preferably alinking group having 1 to 15 carbon atoms. Particularly preferableexamples of the linking group include an alkyleneoxy group having 1 to25 carbon atoms (more preferably 1 to 10 carbon atoms), an imino group(—NH—), a sulfamoyl group, a divalent linking group including analkylene group such as an alkylene group having 1 to 20 carbon atoms(more preferably 1 to 15 carbon atoms) or an ethylene oxide group[—(CH₂CH₂O)_(n)—, n=1 to 6], and a combination of two or more thereof.

Ar¹ represents a monovalent group derived from a condensed aromatic ringhaving 8 or more carbon atoms, a heterocycle having an aromatic ringcondensed therein, or a compound having two or more benzene rings linkedto each other.

The “condensed aromatic ring having 8 or more carbon atoms” may be anaromatic ring having two or more benzene rings condensed therein or anaromatic ring having 8 or more carbon atoms composed of at least onearomatic ring and a ring formed by an alicyclic hydrocarbon condensedwith the aromatic ring. Specific examples include naphthalene,anthracene, fluorene, phenanthrene, and acenaphthene.

The “heterocycle having an aromatic ring condensed therein” is acompound consisting of a heteroatom-free aromatic compound (preferably abenzene ring) and a heteroatom-containing cyclic compound condensed witheach other. The heteroatom-containing cyclic compound is preferably afive- or six-membered ring. The heteroatom is preferably a nitrogenatom, an oxygen atom or a sulfur atom. The heteroatom-containing cycliccompound may have a plurality of heteroatoms. In this case, theheteroatoms may be the same as or different from each other. Specificexamples of the heterocycle having an aromatic ring condensed thereininclude phthalimide, acridone, carbazole, benzoxazole, andbenzothiazole.

Examples of the compound having two or more benzene rings linked to eachother include compounds having two or more benzene rings linked to eachother via a single bond or a linking group having 1 or 2 carbon atoms.

Specific examples of the monovalent group derived from a compound havingtwo or more benzene rings linked to each other include a biphenyl group,a terphenyl group, a diphenylmethyl group, a triphenylmethyl group andthe like.

Specific examples of monomers that forms the structural unit representedby Formula (1) include the following monomers. The present invention isnot limited to these monomers.

M-25/M-27 represents a mixture of monomers M-25 and M-27, each of whichhas the substituent at m- or p-position.

M-28/M-29 represents a mixture of monomers M-28 and M-29, each of whichhas the substituent at m- or p-position.

Ar¹ in the structural unit represented by Formula (1) is preferably amonovalent group derived from acridone or phthalimide from the viewpointof the dispersion stability of the coated pigment, and more preferably amonovalent group derived from acridone.

As the structural unit represented by Formula (1), from the viewpoint ofdispersion stability of the pigment, a structural unit that is specifiedby selecting an unsubstituted phenylene group as L₁, a divalent linkinggroup (preferably methylene) as L₂, and a monovalent group derived fromacridone as Ar¹ is preferable.

The content of the structural unit represented by Formula (1) in thecopolymer is preferably in the range of from 5% by mass to 25% by mass,with respect to the total mass of the copolymer, and more preferably inthe range of from 10% by mass to 18% by mass.

When the content is 5% by mass or more, generation of image defects suchas white spots tends to be suppressed markedly desirably, on the otherhand, when the content is 25% by mass or less, problems of productionsuitability caused by lowering the solubility of the copolymer in apolymerization reaction liquid (for example, methyl ethyl ketone) tendnot to be brought about desirably.

The water-insoluble resin in the preferable exemplary embodiment of theinvention may include a structural unit represented by the followingFormula (2) other than the structural unit represented by Formula (1).

In Formula (2), R² represents a hydrogen atom or a methyl group, andpreferably a methyl group. Ar² represents a monovalent group derivedfrom an unsubstituted or substituted aromatic ring (aromatic ringgroup). When the aromatic ring is substituted by a substituent, examplesof the substituent include a halogen atom, an alkyl group, an alkoxygroup, a hydroxy group, a cyano group and, an alkoxycarbonyl group, andthe aromatic ring may form a condensed ring. When the aromatic ringforms a condensed ring, the condensed ring may be, for example, acondensed aromatic ring having 8 or more carbon atoms, or an aromaticring having a heterocycle condensed therein. Further, Ar² may be amonovalent group derived from a compound having two or more aromaticrings linked to each other.

In Formula (2), each of “a condensed aromatic ring having 8 or morecarbon atoms” and “an aromatic ring having a heterocycle condensedtherein” has the same definition as “a condensed aromatic ring having 8or more carbon atoms” and “an aromatic ring having a heterocyclecondensed therein” in Formula (1) respectively. Further, “a monovalentgroup derived from a compound having two or more aromatic rings linkedto each other” in Formula (2) preferably includes “a monovalent groupderived from a compound having two or more aromatic rings linked to eachother” in Formula (1).

The aromatic ring group represented by Ar² is linked via an ester groupand an ethylene oxide chain to the main chain of the water-insolubleresin, and the aromatic ring group is not directly linked to the mainchain, and thus a suitable distance is maintained between thehydrophobic aromatic ring and the hydrophilic structural unit, so thatthe water-insoluble resin interacts readily with, and is adsorbed firmlyonto, a pigment to improve dispersibility.

In particular, the aromatic ring group represented by Ar² is preferablyan unsubstituted phenyl group or an unsubstituted naphthyl group, andparticularly preferably an unsubstituted phenyl group.

n is an average repeating number of the ethyleneoxy units in thewater-insoluble resin used for the resin-coated pigment contained in theaqueous ink composition. n is in the range of 1 to 6, and preferably 1to 2.

Specific examples of monomers that forms the structural unit representedby Formula (2) include the following monomers.

From the viewpoint of dispersion stability, it is particularlypreferable that in the structural unit represented by Formula (2), R² isa methyl group, Ar² is an unsubstituted phenyl group, and n is 1 to 2.

The content of the structural unit of Formula (1) in the water-insolubleresin is preferably in the range of 30% by mass to 70% by mass, and morepreferably in the range of 40% by mass to 50% by mass, based on thetotal mass of the water-insoluble resin. When the content is 30% by massor more, dispersibility is good, and when the content is 70% by mass orless, the adhesion and deposition of the aggregate may be prevented, theremovability of adhered aggregate (maintenance properties) is good, andgeneration of imaging defects such as white spots may be prevented.

The water-insoluble resin in the exemplary embodiment of the inventionis preferably a resin including a hydrophilic structural unit (A) and ahydrophobic structural unit (B), from the viewpoint of allowing thewater-insoluble resin to be stably present in an aqueous ink, to reduceadhesion or deposition of the aggregate, and to facilitate removal ofthe adhered aggregate. Herein, the hydrophobic structural unit (B)preferably includes the structural unit represented by Formula (1) orFormula (2) above.

The water-insoluble resin of the present invention may further have anadditional hydrophobic structural unit (B′) other than the structuralunit represented by Formula (1) and the structural unit represented byFormula (2). Examples of the hydrophobic structural unit (B′) mayinclude a structural units derived from vinyl monomers such as(meth)acrylates, (meth)acrylamides, styrenes or vinylesters which do notbelong to the hydrophilic structural unit (A) (for example, those havingno hydrophilic functional group), a hydrophobic structural unit havingan aromatic ring that is linked to an atom of the main chain thereofthrough a linking group, and the like. These structural units may beused one kind alone or two or more kinds in combination.

Examples of the (meth)acrylates include methyl (meth)acrylate, ethyl(meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, and hexyl(meth)acrylate. Among them, methyl (meth)acrylate, ethyl (meth)acrylate,and butyl (meth)acrylate are preferable, and methyl (meth)acrylate andethyl (meth)acrylate are particularly preferable.

Examples of the (meth)acrylamides include N-cyclohexyl (meth)acrylamide,N-(2-methoxyethyl) (meth)acrylamide, N,N-diallyl (meth)acrylamide, andN-allyl (meth)acrylamide.

Examples of the styrenes include styrene, methylstyrene,dimethylstyrene, trimethylstyrene, ethylstyrene, isopropylstyrene,n-butylstyrene, tert-butylstyrene, methoxystyrene, butoxystyrene,acetoxystyrene, chlorostyrene, dichlorostyrene, bromostyrene,chloromethylstyrene, hydroxystyrene protected by a group removable withan acidic substance (for example, t-Boc), methyl vinyl benzoate,α-methylstyrene, and vinylnaphthalene. Among them, styrene andα-methylstyrene are preferable.

Examples of the vinyl esters include vinyl acetate, vinyl chloroacetate,vinyl propionate, vinyl butyrate, vinyl methoxyacetate, and vinylbenzoate. Among them, vinyl acetate is preferable.

The above-described “hydrophobic structural unit containing an aromaticring that is linked to an atom in the main chain via a linking group” ispreferably a structural unit wherein the proportion of the aromatic ringlinked to an atom in the main chain of the copolymer via a linking groupis from 15% by mass to 27% by mass, more preferably from 15% by mass to25% by mass, and even more preferably from 15% by mass to 20% by masswith respect to the copolymer.

The aromatic ring is linked to the atom in the main chain of thecopolymer not directly but via a linking group. Therefore, an adequatedistance is kept between the hydrophobic aromatic ring and thehydrophilic structural unit, so that the copolymer readily interactswith the pigment and is firmly adsorbed thereon, thus improving thedispersibility of the pigment.

The “hydrophobic structural unit containing an aromatic ring that islinked to an atom in the main chain via a linking group” is preferably astructural unit represented by the following Formula (3) (excluding thestructural unit represented by Formula (1) and the structural unitrepresented by Formula (2)).

Formula (3)

In Formula (3), R¹¹represents a hydrogen atom, a methyl group, or ahalogen atom. L¹¹ represents *—COO—, *—COO—, *—CONR¹²—, or *—O—, and R¹²represents a hydrogen atom or an alkyl group having 1 to 10 carbonatoms. In the group represented by L¹¹, an asterisk (*) denotes a bondconnected to the main chain.

L¹² represents a single bond or a divalent linking group having 1 to 30carbon atoms. When L¹² is a divalent linking group, it is preferably alinking group having 1 to 25 carbon atoms, more preferably a linkinggroup having 1 to 20 carbon atoms, and even more preferably a linkinggroup having 1 to 15 carbon atoms.

Among them, particularly preferable examples include an alkyleneoxygroup having 1 to 25 (more preferably 1 to 10 carbon atoms) carbonatoms, an imino group (—NH—), a sulfamoyl group, and divalent linkinggroups containing an alkylene group, such as an alkylene group having 1to 20 carbon atoms (more preferably 1 to 15 carbon atoms) or an ethyleneoxide group [—(CH₂CH₂O)_(n)—, n=1 to 6], and combinations of two or moreof these groups.

In Formula (3), Ar¹¹ represents a monovalent group derived from anaromatic ring.

The aromatic ring group which derives the monovalent group representedby Ar¹¹ is not particularly limited, and examples of the aromatic ringinclude a benzene ring, a condensed aromatic ring having eight or morecarbon atoms, an aromatic ring condensed with a heterocycle, and acompound having two or more benzene rings linked to each other. Thedetails about the condensed aromatic ring having eight or more carbonatoms, the aromatic ring condensed with a heterocycle, and a compoundhaving two or more benzene rings linked to each other have beendescribed above.

Specific examples of a monomer capable of forming the “hydrophobicstructural unit containing an aromatic ring that is linked to an atom inthe main chain via a linking group” are shown below. However, theinvention is not limited to the following specific examples.

The water-insoluble resin of the present invention is, among the above,preferably characterized in that the hydrophilic structural unit (A) is(meth)acrylic acid and the hydrophobic structural unit (B) is at leastone kind selected from (i) a structural unit represented by Formula (1)(preferably a structural unit derived from the foregoing M-25/M-27 orM-28/M-29), (ii) a structural unit represented by Formula (2)(preferably a structural unit derived from phenoxyethyl (meth)acrylate),and (iii) a hydrophobic structural unit (B′) other than the foregoingstructural units (preferably a structural unit derived from methyl(meth)acrylate, ethyl (meth)acrylate, or benzyl methacrylate).

Furthermore, the water-insoluble resin of the present invention ispreferably characterized in that the hydrophilic structural unit (A) is(meth)acrylic acid and the hydrophobic structural unit (B) contains atleast one kind of the above (i) and (ii).

Particularly, the water-insoluble resin of the present invention ispreferably characterized in that the hydrophilic structural unit (A) is(meth)acrylic acid and the hydrophobic structural unit (B) contains atleast one kind of the above (i) and (ii) and further contains (iii).

In the water-insoluble resin in the exemplary embodiment of theinvention, although the ratio of the hydrophilic structural unit (A) tothe hydrophobic structural unit (B) (including the structural unitrepresented by Formula (2), the structural unit represented by Formula(1) and the other hydrophobic structural units (B′) depends on thedegrees of the hydrophilicity and hydrophobicity of these components,the content of the hydrophilic structural units (A) in thewater-insoluble resin is preferably 15% by mass or less. The content ofthe hydrophobic structural units (B) is preferably more than 80% bymass, and more preferably 85% by mass or more with respect to the totalmass of the water-insoluble resin.

When the content of the hydrophilic structural unit (A) is 15% by massor less, the amount of the component that dissolves itself in theaqueous medium is decreased, which results in the improvement of pigmentproperties such as dispersibility, whereby good ink ejection propertiesare achieved during inkjet recording.

The content ratio of the hydrophilic structural unit (A) is preferablymore than 0% by mass but 15% by mass or less, more preferably from 2% bymass to 15% by mass, even more preferably from 5% by mass to 15% bymass, and particularly preferably from 8% by mass to 12% by mass withrespect to the total mass of the water-insoluble resin.

In embodiments, the acid value of the water-insoluble resin ispreferably from 30 mgKOH/g to 100 mgKOH/g, more preferably from 30mgKOH/g to 85 mgKOH/g, and particularly preferably from 50 mgKOH/g to 85mgKOH/g from the viewpoints of pigment dispersibility and storagestability.

The acid value is defined as the mass (mg) of KOH necessary forcompletely neutralizing 1 g of the water-insoluble resin, and measuredby the method described in Japanese Industrial Standard (JIS K0070,1992), the disclosure of which is incorporated by reference herein.

The weight average molecular weight (Mw) of the water-insoluble resin inthe exemplary embodiment of the invention is preferably 30,000 or more,more preferably from 30,000 to 150,000, even more preferably from 30,000to 100,000, and particularly preferably from 30,000 to 80,000. If themolecular weight is 30000 or more, the water-insoluble resin may providea good steric repulsion effect as a dispersant, and is readily adsorbedon the pigment owing to the steric effect.

The number average molecular weight (Mn) of the water-insoluble resin ispreferably about 1,000 to about 100,000, and particularly preferablyabout 3,000 to about 50,000. When the number average molecular weight iswithin the above-described range, the water-insoluble resin may serve asa coating on the pigment or a coating of the ink composition. Thewater-insoluble resin in the exemplary embodiment of the invention ispreferably used in the form of an alkali metal salt or an organic aminesalt.

The molecular weight distribution of the water-insoluble resin in theexemplary embodiment of the invention (weight average molecularweight/number average molecular weight) is preferably from 1 to 6, andmore preferably from 1 to 4. When the molecular weight distribution iswithin the above-described range, the resulting ink has improveddispersion stability and ejection stability.

The number average molecular weight and the weight average molecularweight are measured by the differential refractometer detection with THFas a solvent in a GPC analyzer using columns TSKgel Super HZM-H, TSKgelSuper HZ4000 and TSKgel Super HZ2000 (trade name; all manufactured byTosoh Corporation), and is obtained in terms of polystyrene used as areference material.

The water-insoluble resin in the exemplary embodiment of the inventionmay be synthesized by any polymerization method, for example, solutionpolymerization, precipitation polymerization, suspension polymerization,bulk polymerization, or emulsion polymerization. The polymerizationreaction may be carried out under a known system, such as a batch,semi-continuous, or continuous system. Initiation of the polymerizationmay be carried out with a radical initiator, or photoirradiation orradiation-irradiation. These methods of polymerization and initiation ofpolymerization are described in, for example, “Kobunshi Gosei Hoho” byTeiji Tsuruta, Revised Edition (published by Nikkan Kogyo Shimbun, Ltd.,1971) and “Kobunshi Gosei no Jikkenho” by Takayuki Ohtu and MasaetuKinoshita (published by Kagaku-Dojin Publishing Company Inc., 1972)pages 124 to 154.

Among these polymerization methods, a solution polymerization methodusing a radical initiator is preferable. Examples of the solvent used inthe solution polymerization method include various organic solvents suchas ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, methylisobutyl ketone, cyclohexanone, tetrahydrofuran, dioxane,N,N-dimethylformamide, N,N-dimethylacetamide, benzene, toluene,acetonitrile, methylene chloride, chloroform, dichloroethane, methanol,ethanol, 1-propanol, 2-propanol, and 1-butanol. These solvents may beused alone or in a combination of two or more of them, or may be mixedwith water as a mixed solution. The polymerization temperature should bechosen in consideration of the molecular weight of the intended polymerand the type of the initiator, and is usually from 0° C. to 100° C., andis preferably from 50° C. to 100° C. The reaction pressure may beappropriately selected, and is usually from 1 kg/cm² to 100 kg/cm², andparticularly preferably from about 1 kg/cm² to about 30 kg/cm². Thereaction period may be about 5 hours to about 30 hours. The resultingresin may be subjected to purification treatment such asreprecipitation.

Specific examples of preferable water-insoluble resins in the exemplaryembodiment of the invention are shown below. The invention is notlimited to these examples. In the following Formula, a, b and c eachindependently represent the content of the correspondent structural unit% by mass in the polymer.

R¹¹ n R²¹ R³¹ R³² a b c Mw B-1 CH₃ 1 CH₃ CH₃ —CH₃ 60  9 31 35500 B-2 H 1H H —CH₂CH₃ 69 10 21 41200 B-3 CH₃ 2 CH₃ CH₃ —CH₃ 70 11 19 68000 B-4 CH₃4 CH₃ CH₃ —CH(CH₃)CH₃ 70  7 23 72000 B-5 H 5 H H —CH₃ 70 10 20 86000 B-6H 5 H H —CH₂CH(CH₃)CH₃ 70  2 28 42000 B-7 CH₃ 1 CH₃ CH₃ —CH₂CH₃ 50 11 3944500 B-8 CH₃ 1 CH₃ CH₃ —CH₂CH₃ 50 10 40 51200 B-9 H 1 H H —CH₂CH₃ 45 1144 48900  B-10 H 1 CH₃ CH₃ —CH₂CH₃ 45 12 43 43600

Mw B-11

72400 B-12

33800 B-13

39200

The weight ratio (p:r) between the pigment (p) and the water-insolubleresin (r) in the exemplary embodiment of the invention is preferablyfrom 100:25 to 100:140, and more preferably from 100:25 to 100:50. Whenthe proportion of the water-insoluble resin is 25 or more, dispersionstability and abrasion resistance tend to improve, and when 140 or less,dispersion stability tends to improve.

The resin-coated pigment (capsulated pigment) in the exemplaryembodiment of the invention may be produced using a water-insolubleresin and a pigment by a known physical or chemical method such as thatdescribed in JP-A Nos. 9-151342, 10-140065, 11-209672, 11-172180,10-25440, and 11-43636. Specific examples of the method include thephase inversion method and acid precipitation method described in JP-ANos. 9-151342 and 10-140065. Of these methods, the phase inversionmethod is preferable from the viewpoint of dispersion stability.

Basically, the phase inversion method is a self dispersion (phaseinversion emulsification) method comprising dispersing in water a mixedmelt of a pigment and a resin having self dispersibility or solubility.The mixed melt may contain a curing agent or a polymer compound. Themixed melt refers to a state where undissolved components are mixedand/or a state where dissolved components are mixed. Details about the“phase inversion method” are described in JP-A No. 10-140065.

In the ink composition in the exemplary embodiment of the invention, theresin-coated pigment is preferably prepared using the water-insolubleresin through a preparation method of preparing a dispersion of theresin-coated pigment including, for example, the following steps (1) and(2). The ink composition of the exemplary embodiment of the inventionmay be prepared by preparing a dispersion of the resin-coated pigment inaccordance with the above-described preparation method, followed bypreparing an ink composition from the obtained dispersion of theresin-coated pigment, water, and a hydrophilic organic solvent.

Step (1): a mixture containing a water-insoluble resin including thestructural unit having an acidic group, an organic solvent, aneutralizing agent, a pigment, and water is dispersed with a stirrer orthe like to obtain a dispersion.

Step (2): at least a part of the organic solvent is removed from thedispersion.

The stirring method is not particularly limited, and may use a commonmixing stirrer or, if necessary, a disperser such as an ultrasonicdisperser, a high-pressure homogenizer, or a bead mill.

Examples of the organic solvent preferable herein include alcoholsolvents, ketone solvents, and ether solvents. Examples of the alcoholsolvents include isopropyl alcohol, n-butanol, t-butanol, and ethanol.Examples of the ketone solvents include acetone, methyl ethyl ketone,diethyl ketone, and methyl isobutyl ketone. Examples of the ethersolvents include dibutyl ether and dioxane. Among these solvents, ketonesolvents such as methyl ethyl ketone and alcohol solvents such asisopropyl alcohol are preferable, and methyl ethyl ketone is morepreferable.

The neutralizing agent may be preferably used in the process (1) forneutralizing a part or all of the acidic groups so that thewater-insoluble resin can form a stable emulsion or dispersion in water.Examples of the neutralizing agent include alcohol amines (such asdiethanolamine, triethanolamine, and 2-amino-2-ethyl-1,3-propanediol),alkali metal hydroxides (such as lithium hydroxide, sodium hydroxide,and potassium hydroxide), ammonium hydroxide (such as ammonium hydroxideand quaternary ammonium hydroxide), phosphonium hydroxides, and alkalimetal carbonates. Among them, sodium hydroxide and potassium hydroxidemay be preferably used.

The water-insoluble resin may have a neutralization degree of from 70%to 95%. When the neutralization degree is 70% or higher, generation ofwhite spots in an image formed from the ink may be suppressed. When theneutralization degree is 95% or lower, abrasion resistance of an imageformed from the ink may be improved.

The neutralization degree may be preferably from 70% to 90%, and morepreferably from 75% to 90%. By adjusting the neutralization degreewithin the above range, generation of white spots in an image formedfrom the ink may be effectively suppressed, and abrasion resistance ofan image formed from the ink may be effectively improved.

The “neutralization degree” herein referred is a ratio (%) of anequivalent of a neutralizer with respect to one equivalent of the acidgroup. Namely, the neutralization degree of the water-insoluble resin isdefined as a ratio of the total equivalence of the neutralizer to thetotal equivalence of the acid group contained in the water-insolubleresin, and is obtained in accordance with the following equality.Neutralization degree of water-insoluble resin=(total equivalence ofneutralizer)/total equivalence of acid group in water-insolubleresin)×100(%)

In the process (2), the organic solvent is evaporated from thedispersion prepared in the process (1) by a common procedure such asvacuum distillation to convert the phase into a water system, therebyobtaining a dispersion of resin-coated pigment particles, the particlesurface of the pigment being coated with the water-insoluble resin. Theobtained dispersion is substantially free from the organic solvent. Theamount of the organic solvent may be preferably 0.2% by mass or less,and more preferably 0.1% by mass or less.

More specifically, the method for forming the dispersion of thewater-insoluble resin may include: (1) mixing an acid group-containingwater-insoluble resin or its solution in an organic solvent with a basiccompound (neutralizing agent), thereby carrying out neutralization; (2)mixing the obtained mixed solution with a pigment to make a suspension,and then subjecting the suspension to dispersing by using a disperser orthe like to obtain a pigment dispersion; and (3) removing the organicsolvent by, for example, distillation, thereby coating the pigment witha water-insoluble resin having a structural unit having an acid group,and dispersing the coated pigment particles in an aqueous medium toprovide an aqueous dispersion.

The method is further specifically described in JP-A Nos. 11-209672 and11-172180.

The dispersing may be carried out by using, for example, a ball mill, aroll mill, a bead mill, a high-pressure homogenizer, a high-speedstirring disperser, or an ultrasonic homogenizer.

The average particle diameter of the pigment covered with thewater-insoluble resin may be preferably in the range of 10 nm to 200 nm,more preferably in the range of 10 nm to 150 nm, and even morepreferably in the range of 10 nm to 100 nm. When the average particlediameter is 200 nm or less, the color reproducibility and dottingproperty of the ink under inkjet recording system may become favorable.When the average particle diameter is 10 nm or more, light fastness maybecome favorable.

There is no particular limitation to the particle size distribution ofthe pigment covered with the water-insoluble resin. The polymerparticles may have either a broad particle size distribution or amonodisperse particle size distribution. Two or more colored particles,each of which having a monodisperse particle size distribution, may beused in combination as a mixture.

The average particle diameter and the particle size distribution of thepigment covered with the water-insoluble resin may be measured by, forexample, the dynamic light scattering method.

The pigment covered with the water-insoluble resin may be used singly orin a combination of two or more thereof.

From the viewpoint of the density of an image formed from the inkcomposition, the content of the pigment covered with the water-insolubleresin in the ink composition may be preferably from 0.1% by mass to 25%by mass, more preferably from 1% by mass to 20% by mass, even morepreferably from 1.5% by mass to 15% by mass, and further preferably from1.5% by mass to 10% by mass, with respect to the total amount of the inkcomposition.

The ratio of the content of colloidal silica to the content of thewater-insoluble resin (colloidal silica/water-insoluble resin) in theink composition may be preferably from 0.0001 to 0.5, more preferablyfrom 0.0001 to 0.3, and even more preferably from 0.001 to 0.05, interms of mass from the viewpoints of suppression of shape deformationdue to erosion of the nozzle plate and suppression of deterioration ofthe liquid-repellency of the inkjet head member.

In embodiments which may be preferable in view of ink ejectionreliability, abrasion resistance of an image formed from the inkcomposition, and suppression of deterioration of the liquid-repellencyof the inkjet head member, the water-insoluble resin may have an acidvalue of from 50 mgKOH/g to 90 mgKOH/g, the colloidal silica may have avolume-average particle diameter of from 3 nm to 50 nm, and the ratio ofthe content of colloidal silica to the content of the water-insolubleresin (colloidal silica/water-insoluble resin) may be from 0.0001 to0.3; and in more preferable embodiments, in the ink composition, thewater-insoluble resin may have an acid value of from 55 mgKOH/g to 80mgKOH/g, the colloidal silica may have a volume-average particlediameter of from 3 nm to 25 nm, and the ratio of the content ofcolloidal silica to the content of the water-insoluble resin (colloidalsilica/water-insoluble resin) may be from 0.001 to 0.05.

[Hydrophilic Organic Solvent]

The ink composition of the exemplary embodiment of the inventionpreferably includes a water-based medium. The water-based mediumcontains at least water as a solvent, but preferably contains water andat least one hydrophilic organic solvent. The hydrophilic organicsolvent is capable of enhancing effects such as anti-drying, wetting, orpenetration promoting.

An anti-drying agent or a wetting agent is used for the purpose ofpreventing the clogging caused as the ink for inkjet recording dries upat the ink spray orifice of a nozzle. The anti-drying agent or wettingagent is preferably a hydrophilic organic solvent having a lower vaporpressure than water.

Furthermore, for the purpose of making the ink composition penetrateeasily into paper, a hydrophilic organic solvent is suitably used as apenetration promoting agent.

The ink composition of the exemplary embodiment of the inventionpreferably includes at least one type of a first hydrophilic organicsolvent having an I/O value of from 0.70 to less than 1.0. When the I/Ovalue of the first hydrophilic organic solvent is less than 1.00,compatibility with the self-dispersing polymer particles is enhanced,the fixability of the image formed is more effectively enhanced, and theabrasion resistance of the image is further enhanced. When the I/O valueof the first hydrophilic organic solvent is 0.70 or more, the stabilityof the ink composition is enhanced.

The I/O value of the hydrophilic organic solvent has the same definitionas that in the self-dispersing polymer which is described below, and iscalculated in a manner substantially similar to that in the calculationof the I/O value for the self-dispersing polymer.

It is preferable that the ink composition of the exemplary embodiment ofthe invention further includes at least one of a second hydrophilicorganic solvent having an I/O value of 1.00 to 1.50, in addition to thefirst hydrophilic organic solvent. When the I/O value of the secondhydrophilic organic solvent is 1.00 or more, the stability of the inkcomposition is more effectively enhanced. When the I/O value of thesecond hydrophilic organic solvent is 1.50 or less, deterioration of thefixation properties of the formed image can be suppressed.

Specific examples of the first hydrophilic organic solvent having an I/Ovalue of 0.70 or more and less than 1.00 include glycol ethers.Propylene glycol ether or ethylene glycol ether is preferable, andpropylene glycol ether is more preferable. Specific examples includetriprolene glycol monomethyl ether (I/O value: 0.80), triprolene glycolmonoethyl ether (I/O value: 0.73), triprolene glycol monobutyl ether(I/O value: 0.61), diprolene glycol monoethyl ether (I/O value: 0.78),diprolene glycol monobutyl ether (I/O value: 0.70), and prolene glycolmonobutyl ether (I/O value: 0.88).

Among these, triprolene glycol monomethyl ether (I/O value: 0.80) ispreferable from the viewpoints of image fixability and ink stability.

Specific examples of the second hydrophilic organic solvent having anI/O value of 1.0 to 1.5, include propylene glycol monomethyl ether (I/Ovalue: 1.50), propylene glycol monoethyl ether (I/O value: 1.20),diethylene glycol monobutyl ether (I/O value: 1.40), triethylene glycolmonobutyl ether (I/O value: 1.20), 2,2-diethyl-1,3-propanediol (I/Ovalue: 1.43), 2-methyl-2-propyl-1,3-propanediol (I/O value: 1.43),2,4-dimethyl-2,4-pentanediol (I/O value: 1.43),2,5-dimethyl-2,5-hexanediol (I/O value: 1.25), tripropylene glycol (I/Ovalue: 1.33), SANNIX GP250 (trade name, I/O value: 1.30, manufactured bySanyo Chemical Industries, Ltd.), and the like. Among them, SANNIX GP250is preferable from the viewpoints of image fix properties and inkstability.

The content of the first hydrophilic organic solvent in the inkcomposition for inkjet recording of the exemplary embodiment of theinvention is preferably 0.1% by mass to 20% by mass, more preferably 1%by mass to 16% by mass, and further preferably 2% by mass to 12% bymass, from the viewpoints of image fix properties and ink stability.

Furthermore, it is preferable that the ink composition includes, as thefirst hydrophilic organic solvent, a hydrophilic organic solvent whoseI/O value is selected from the range of 0.70 or more and less than 1.00,in an amount of 1 to 16% by mass, and it is more preferable that the inkcomposition includes a hydrophilic organic solvent whose I/O value isselected from the range of 0.70 or more and less than 0.90, in an amountof 2% by mass to 12% by mass.

The content of the second hydrophilic organic solvent in the inkcomposition for inkjet recording of the exemplary embodiment of theinvention is preferably 0.1% by mass to 20% by mass, more preferably 1%by mass to 16% by mass, and further preferably 2% by mass to 12% bymass, from the viewpoints of image fix properties and ink stability.

Furthermore, it is preferable that the ink composition includes, as thesecond hydrophilic organic solvent, a hydrophilic organic solvent whoseI/O value is selected from the range of 1.00 to 1.50, in an amount of 1%by mass to 16% by mass, and it is more preferable that the inkcomposition includes a hydrophilic organic solvent whose I/O value isselected from the range of 1.20 to 1.40, in an amount of 2% by mass to12% by mass.

Furthermore, the content ratio of the second hydrophilic organic solventto the first hydrophilic organic solvent in the ink composition forinkjet recording of the exemplary embodiment of the invention (secondhydrophilic organic solvent/first hydrophilic organic solvent) ispreferably 1/10 to 10/1, more preferably 1/4 to 4/1, and furtherpreferably 1/2 to 2/1, from the viewpoints of image fix properties andink stability.

The ink composition of the exemplary embodiment of the invention mayfurther include another hydrophilic organic solvent, in addition to thefirst hydrophilic organic solvent and the second hydrophilic organicsolvent. As for the other hydrophilic organic solvent, polyhydricalcohols are useful for the purpose of functioning as an anti-dryingagent or a wetting agent, and examples include glycerin (I/O value:5.00), ethylene glycol (I/O value: 2.00), diethylene glycol (I/O value:5.00), triethylene glycol (I/O value: 3.43), propylene glycol (I/Ovalue: 2.50), dipropylene glycol (I/O value: 2.00), 1,3-butanediol (I/Ovalue: 2.50), 2,3-butanediol (I/O value: 2.50), 1,4-butanediol (I/Ovalue: 2.50), 3-methyl-1,3-butanediol (I/O value: 2.00), 1,5-pentanediol(I/O value: 2.00), tetraethylene glycol (I/O value: 2.91),1,6-hexanediol (I/O value: 1.67), 2-methyl-2,4-pentanediol (I/O value:1.67), polyethylene glycol (I/O value depends on the number ofrepetition of the ethylene chain), 1,2,4-butanetriol (I/O value: 3.75),1,2,6-hexanetriol (I/O value: 2.50), and the like. These may be usedindividually, or may be used in combination of two or more types.

For the purpose of functioning as a permeation agent, a polyol compoundis preferable, and preferable examples of aliphatic diol include2-ethyl-2-methyl-1,3-propanediol (I/O value: 1.67),3,3-dimethyl-1,2-butanediol (I/O value: 1.67), 5-hexene-1,2-diol,2-ethyl-1,3-hexanediol (I/O value: 2.00), and2,2,4-trimethyl-1,3-pentanediol (I/O value: 1.88).

The content of the other hydrophilic organic solvent may be, forexample, 16% by mass or less, and is preferably 12% by mass or less, andmore preferably 8% by mass or less.

The hydrophilic organic solvent in the ink composition of the exemplaryembodiment of the invention may be used individually, or may be used asmixtures of two or more types. The content of the hydrophilic organicsolvent is preferably 1% by mass to 60% by mass, more preferably 5% bymass to 40% by mass, and particularly preferably 10% by mass to 30% bymass, from the viewpoints of stability and ejection properties.

The amount of addition of water used in the exemplary embodiment of theinvention is not particularly limited, but the amount is preferably 10%by mass to 99% by mass, more preferably 30% by mass to 80% by mass, andfurther preferably 50% by mass to 70% by mass, in the ink composition,from the viewpoints of securing stability and ejection reliability.

(Resin Particles)

An ink composition according to the exemplary embodiment of theinvention preferably includes at least one kind of resin particles fromviewpoints of fixability of image formed, abrasion resistance of theimage, and aggregation property of the ink composition. Further, theresin particles are more preferably particles of self-dispersingpolymers.

The self-dispersing polymer according to the exemplary embodiment of theinvention means a water-insoluble polymer which can be in a dispersedstate in an aqueous medium due to the functional group (particularly, anacidic group or a salt thereof) of the polymer itself when brought to adispersed state by an phase inversion emulsification method in theabsence of a surfactant.

Here, the term dispersed state includes both an emulsified state(emulsion) in which a water-insoluble polymer is dispersed in an aqueousmedium in the liquid state, and a dispersed state (suspension) in whicha water-insoluble polymer is dispersed in an aqueous medium in the solidstate.

In regard to the self-dispersing polymer according to the exemplaryembodiment of the invention, it is preferable that the water-insolublepolymer is a self-dispersing polymer capable of being in a dispersedstate in the solid state, from the viewpoint of ink fixation propertiesobtainable when incorporated in an ink composition.

The method for preparing the emulsified or dispersed state of theself-dispersing polymer, that is, an aqueous dispersion of theself-dispersing polymer, may be a phase inversion emulsification method.The phase inversion emulsification method may be, for example, a methodof dissolving or dispersing the self-dispersing polymer into a solvent(for example, a hydrophilic organic solvent or the like), subsequentlyintroducing the solution or dispersion directly into water withoutadding a surfactant, mixing under stirring the system while asalt-producing group (for example, an acidic group) carried by theself-dispersing polymer is neutralized, removing the solvent, and thenobtaining an aqueous dispersion that has been brought to an emulsifiedor dispersed state.

A stable emulsified or dispersed state for the self-dispersing polymerof the exemplary embodiment of the invention means that even when asolution prepared by dissolving 30 g of a water-insoluble polymer in 70g of an organic solvent (for example, methyl ethyl ketone), aneutralizing agent capable of neutralizing 100% of the salt-producinggroup of the water-insoluble polymer (if the salt-producing group isanionic, sodium hydroxide, and if the salt-producing group is cationic,acetic acid), and 200 g of water are mixed and stirred (apparatus: astirring apparatus equipped with a stirring blade, speed of rotation 200rpm, for 30 minutes, 25° C.), and then the organic solvent is removedfrom the liquid mixture, the emulsified or dispersed state remainsstable for at least one week at 25° C., so that the generation ofprecipitates cannot be verified by visual inspection.

The stability of the emulsified or dispersed state for theself-dispersing polymer can be confirmed by a precipitation accelerationtest based on centrifugation. The stability obtained by a precipitationacceleration test based on centrifugation can be evaluated by, forexample, adjusting the aqueous dispersion of the polymer particlesobtained by the method described above to a solids concentration of 25%by mass, subsequently centrifuging the dispersion for one hour at 12,000rpm, and measuring the solids concentration of the supernatant obtainedafter centrifugation.

When the ratio of the solids concentration after centrifugation to thesolids concentration before centrifugation is large (a value close to1), it means that precipitation of the polymer particles resulting fromcentrifugation does not occur, that is, the aqueous dispersion of thepolymer particles is more stable. According to the present invention,the ratio of the solids concentration before and after centrifugation ispreferably 0.8 or greater, more preferably 0.9 or greater, andparticularly preferably 0.95 or greater.

Further, the water-insoluble polymer means a polymer showing an amountof dissolution of 10 g or less when the polymer is dried at 105° C. for2 hr and then dissolved in 100 g of water at 25° C. The amount ofdissolution is, preferably, 5 g or less and, more preferably, 1 g orless. The amount of dissolution is the amount of dissolution when thepolymer is neutralized with sodium hydroxide or acetic acid to 100% inaccordance with the kind of the salt-forming group of thewater-insoluble polymer.

The self-dispersing polymer according to the exemplary embodiment of theinvention is such that the content of the water-soluble componentexhibiting water-solubility when brought to a dispersed state ispreferably 10% by mass or less, more preferably 8% by mass or less, andeven more preferably 6% by mass or less. When the water-solublecomponent is 10% by mass or less, swelling of the polymer particles orfusion of the polymer particles is effectively suppressed, and a morestable dispersed state can be maintained. Viscosity increase of the inkcomposition can also be suppressed, and the ejection stability becomesbetter when, for example, the ink composition is used for an inkjetrecording method.

Here, the water-soluble component means a compound contained in theself-dispersing polymer, where the compound dissolves in water when theself-dispersing polymer is brought to a dispersed state. Thewater-soluble component is a water-soluble compound that isside-produced or incorporated during the production of theself-dispersing polymer.

The self-dispersing polymer according to the exemplary embodiment of theinvention includes at least one hydrophilic constituent unit derivedfrom a hydrophilic monomer, and at least one hydrophobic constituentunit derived from a hydrophobic monomer. The main chain skeleton of theself-dispersing polymer is not particularly limited, but from theviewpoint of the dispersion stability of the polymer particles, the mainchain skeleton is preferably a vinyl polymer, and preferably a(meth)acrylic polymer. Here, the (meth)acrylic polymer means a polymerincluding at least one of a constituent unit derived from a methacrylicacid derivative and a constituent unit derived from an acrylic acidderivative.

—Hydrophilic Constituent Unit—

The hydrophilic constituent unit in the self-dispersing polymer is notparticularly limited so long as it is derived from a hydrophilicgroup-containing monomer and it may be either a unit derived from onehydrophilic group-containing monomer (hydrophilic monomer) or a unitderived from two or more hydrophilic group-containing monomers. Thehydrophilic group is not particularly limited and it may be either adissociative group or a nonionic hydrophilic group.

The hydrophilic group is preferably a dissociative group from theviewpoints of promoting the self-dispersibility and stability of theformed emulsified or dispersed state and, more preferably, an anionicdissociative group. Examples of the dissociative group include a carboxygroup, a phosphoric acid group, and a sulfonic acid group and, amongthem, a carboxy group is preferred from the viewpoint of the fixingproperty when used in the ink composition.

The hydrophilic group-containing monomer is preferably a dissociativegroup-containing monomer and, preferably, a dissociativegroup-containing monomer having a dissociative group and anethylenically unsaturated bond from the viewpoint ofself-dispersibility.

Examples of the dissociative group-containing monomer include anunsaturated carboxylic acid monomer, an unsaturated sulfonic acidmonomer, and an unsaturated phosphoric acid monomer.

Specific examples of the unsaturated carboxylic acid monomer includeacrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleicacid, fumaric acid, citraconic acid, and 2-(methacryloyloxy)methylsuccinicate, etc. Specific examples of the unsaturated sulfonic acidmonomer include styrenesulfonic acid,2-acrylamido-2-methylpropanesulfonic acid, 3-sulfopropyl (meth)acrylate,and bis(3-sulfopropyl) itaconate. Specific examples of the unsaturatedphosphoric acid monomer include vinylphosphonic acid, vinylphosphate,bis(methacryloyloxyethyl) phosphate, diphenyl-2-acryloyloxyethylphosphate, diphenyl-2-methacryloyloxyethyl phosphate, anddibutyl-2-acryloyloxyethyl phosphate.

Among the dissociative group-containing monomers, an unsaturatedcarboxylic acid monomer is preferred and, at least one kind of acrylicacid and methacrylic acid is more preferred from the viewpoints of thedispersion stability and ejection stability.

Examples of the monomer having a nonionic hydrophilic group includeethylenically unsaturated monomers containing a (poly)ethyleneoxy groupor a polypropyleneoxy group, such as 2-methoxyethyl acrylate,2-(2-methoxyethoxy)ethyl acrylate, 2-(2-methoxyethoxy)ethylmethacrylate, ethoxytriethylene glycol methacrylate, methoxypolyethyleneglycol (molecular weight 200 to 1000) monomethacrylate, and polyethyleneglycol (molecular weight 200 to 1000) monomethacrylate; andethylenically unsaturated monomers having a hydroxyl group, such ashydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate,2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, andhydroxypentyl (meth)acrylate, hydroxyhexyl (meth)acrylate.

The monomer having a nonionic hydrophilic group is preferably anethylenically unsaturated monomer having an alkyl ether at the end,rather than an ethylenically unsaturated monomer having a hydroxyl groupat the end, from the viewpoints of the stability of the particles andthe content of the water-soluble component.

The hydrophilic constituent unit in the self-dispersing polymer ispreferably any of an embodiment containing only a hydrophilicconstituent unit having an anionic dissociative group, and an embodimentcontaining both a hydrophilic constituent unit having an anionicdissociative group and a hydrophilic constituent unit having a nonionichydrophilic group.

Furthermore, an embodiment containing two or more types of hydrophilicconstituent units having an anionic dissociative group, or an embodimenthaving two or more of a hydrophilic constituent unit having an anionicdissociative group and a hydrophilic constituent unit having a nonionichydrophilic group in combination, is also preferable.

The content of the hydrophilic constituent unit in the self-dispersingpolymer is preferably 25% by mass or less, more preferably from 1 to 25%by mass, further preferably from 2 to 23% by mass, and particularlypreferably from 4 to 20% by mass, from the viewpoints of viscosity andstability over time.

When the polymer has two or more types of hydrophilic constituent units,it is preferable that the total content of the hydrophilic constituentunit is within the range described above.

The content of the hydrophilic constituent unit having an anionicdissociative group in the self-dispersing polymer is preferably in therange such that the acid value falls in the suitable range describedbelow.

The content of the constituent unit having a nonionic hydrophilic groupis preferably from 0% by mass to 25% by mass, more preferably from 0% bymass to 20% by mass, and particularly preferably from 0% by mass to 15%by mass, from the viewpoints of ejection stability and stability overtime.

When the self-dispersing polymer has an anionic dissociative group, theacid value (mg KOH/g) is preferably 20 to 200, more preferably 22 to120, and particularly preferably 25 to 100, from the viewpoint ofself-dispersibility, content of the water-soluble component, andfixation properties when the polymer constitutes an ink composition. Theacid value is particularly preferably 30 to 80. When the acid value is20 or greater, the particles can be dispersed more stably, and when theacid value is 200 or less, the content of the water-soluble componentcan be reduced.

—Hydrophobic Constituent Unit—

The hydrophobic constituent unit in the self-dispersing polymer is notparticularly limited so long as it is derived from a hydrophobicgroup-containing monomer (hydrophobic monomer), and may be a constituentunit derived from a monomer containing one type of hydrophobic group, ormay be a constituent unit derived from a monomer containing two or moretypes of hydrophobic groups. The hydrophobic group is not particularlylimited, and may be any of a chain-like aliphatic group, a cyclicaliphatic group, and an aromatic group.

The hydrophobic monomer is preferably such that at least one is a cyclicaliphatic group-containing monomer, and more preferably a cyclicaliphatic group-containing (meth)acrylate (hereinafter, may be referredto as “alicyclic (meth)acrylate”), from the viewpoints of blockingresistance, abrasion resistance and dispersion stability.

The alicyclic (meth)acrylate is a compound including a structural sitederived from (meth)acrylic acid and a structural site derived fromalcohol, and having a structure containing at least one unsubstituted orsubstituted alicyclic hydrocarbon group (cyclic aliphatic group) in thestructural site derived from alcohol. The alicyclic hydrocarbon groupmay be the structural site derived from alcohol itself, or may be linkedto the structural site derived from alcohol via a linking group.

The “alicyclic (meth)acrylate” means a methacrylate or acrylate havingan alicyclic hydrocarbon group.

The alicyclic hydrocarbon group is not particularly limited so long asit contains a cyclic non-aromatic hydrocarbon group, and may be amonocyclic hydrocarbon group, a bicyclic hydrocarbon group, or apolycyclic hydrocarbon group having three or more rings.

Examples of the alicyclic hydrocarbon group include a cycloalkyl groupsuch as a cyclopentyl group or a cyclohexyl group, a cycloalkenyl group,a bicyclohexyl group, a norbornyl group, an isobornyl group, adicyclopentanyl group, a dicyclopentenyl group, an adamantyl group, adecahydronaphthalenyl group, a perhydrofluorenyl group, atricyclo[5.2.1.0^(2,6)]decanyl group, a bicyclo[4.3.0]nonane, and thelike.

The alicyclic hydrocarbon group may be further substituted with asubstituent. Examples of the substituent include an alkyl group, analkenyl group, an aryl group, an aralkyl group, an alkoxy group, ahydroxyl group, a primary amino group, a secondary amino group, atertiary amino group, an alkyl- or arylcarbonyl group, a cyano group,and the like.

The alicyclic hydrocarbon group may further form a condensed ring.

The alicyclic hydrocarbon group according to the exemplary embodiment ofthe invention preferably has 5 to 20 carbon atoms in the alicyclichydrocarbon group moiety, from the viewpoint of viscosity or solubility.

The linking group that links the alicyclic hydrocarbon group and thestructural site derived from alcohol may be suitably an alkylene group,an alkenylene group, an alkynylene group, an arylalkylene group, analkylenoxy group, a mono- or oligoethylenoxy group, a mono- oroligopropylenoxy group, or the like, having 1 to 20 carbon atoms.

Specific examples of the alicyclic (meth)acrylate according to theexemplary embodiment of the invention will be shown below, but theinvention is not limited to these.

Examples of monocyclic (meth)acrylate include cycloalkyl (meth)acrylateshaving a cycloalkyl group having 3 to 10 carbon atoms, such ascyclopropyl (meth)acrylate, cyclobutyl (meth)acrylate, cyclopentyl(meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate,cyclooctyl (meth)acrylate, cyclononyl (meth)acrylate, and cyclodecyl(meth)acrylate.

Examples of bicyclic (meth)acrylate include isobornyl (meth)acrylate,norbornyl (meth)acrylate, and the like.

Examples of tricyclic (meth)acrylate include adamantyl (meth)acrylate,dicyclopentanyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate,and the like.

These can be used individually, or as mixtures of two or more types.

Among these, at least one of the bicyclic (meth)acrylate and thepolycyclic (meth)acrylate having three or more rings is preferable, andat least one selected from isobornyl (meth)acrylate, adamantyl(meth)acrylate and dicyclopentanyl (meth)acrylate is more preferable,from the viewpoints of the dispersion stability of the self-dispersingpolymer particles, and fixability and blocking resistance of an imageformed.

According to the exemplary embodiment of the invention, the content ofthe constituent unit derived from alicyclic (meth)acrylate contained inthe self-dispersing polymer particles is preferably 20% by mass to 90%by mass, more preferably 40% by mass to 90% by mass, and particularlypreferably 50% by mass to 80% by mass, from the viewpoints of thestability of the self-dispersed state, stabilization of particle shapein an aqueous medium due to the hydrophobic interaction between thealicyclic hydrocarbon groups, and a decrease in the amount of thewater-soluble component due to an appropriate hydrophobization ofparticles.

When the content of the constituent unit derived from alicyclic(meth)acrylate is 20% by mass or more, fixation properties and blockingcan be improved. On the other hand, when the content of the constituentunit derived from alicyclic (meth)acrylate is 90% by mass or less, thestability of the polymer particles is improved.

The self dispersing polymer according to the exemplary embodiment of theinvention can be constituted to further include another constituent unitas the hydrophobic constituent unit if necessary, in addition to theconstituent unit derived from alicyclic (meth)acrylate. The monomerforming the other constituent unit is not particularly limited so longas it is a monomer capable of copolymerizing with the alicyclic(meth)acrylate and the hydrophilic group-containing monomer, and anyknown monomer can be used.

Specific examples of the monomer forming the other constituent unit(hereinafter, may be referred to as “other copolymerizable monomer”)include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl(meth)acrylate, isopropyl (meth)acrylate, n-propyl (meth)acrylate,n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate,hexyl (meth)acrylate, and ethylhexyl (meth)acrylate; aromaticring-containing (meth)acrylates such as benzyl (meth)acrylate andphenoxyethyl (meth)acrylate; stryrenes such as styrene, α-methylstyrene,and chlorostyrene; dialkylaminoalkyl (meth)acrylates such asdimethylaminoethyl (meth)acrylate; N-hydroxyalkyl (meth)acrylamides suchas N-hydroxymethyl (meth)acrylamide, N-hydroxyethyl (meth)acrylamide,and N-hydroxybutyl (meth)acrylamide; N-alkoxyalkyl (meth)acrylamidessuch as N-methoxymethyl (meth)acrylamide, N-ethoxymethyl(meth)acrylamide, N-(n-, iso-)butoxymethyl (meth)acrylamide,N-methoxyethyl (meth)acrylamide, N-ethoxyethyl (meth)acrylamide, andN-(n-, iso-)butoxyethyl (meth)acrylamide; and the like.

Among them, the other constituent unit is preferably at least one(meth)acrylate containing a chain-like alkyl group having 1 to 8 carbonatoms, from the viewpoint of the flexibility of the polymer skeleton orthe ease of control of the glass transition temperature (Tg) and fromthe viewpoint of the dispersion stability of the self-dispersingpolymer, and is more preferably a (meth)acrylate having a chain-likealkyl group having 1 to 4 carbon atoms, and particularly preferablymethyl (meth)acrylate or ethyl (meth)acrylate. Here, the chain-likealkyl group refers to an alkyl group having a linear or branched chain.

According to the exemplary embodiment of the invention, a (meth)acrylatecontaining an aromatic group can also be preferably used.

When an aromatic-containing (meth)acrylate is contained as the othercopolymerizable monomer, the content of the constituent unit derivedfrom the aromatic-containing (meth)acrylate is preferably 40% by mass orless, more preferably 30% by mass or less, and particularly preferably20% by mass or less, from the viewpoint of the dispersion stability ofthe self-dispersing polymer particles.

Furthermore, when a styrene-type monomer is used as the othercopolymerizable monomer, the content of the constituent unit derivedfrom the styrene-type monomer is preferably 20% by mass or less, morepreferably 10% by mass or less, and further preferably 5% by mass orless, from the viewpoint of stability when the self-dispersing polymeris made into particles, and it is particularly preferable that thepolymer does not include a constituent unit derived from a styrene-typemonomer.

Here, the styrene-type monomer refers to styrene, substituted styrene(α-methylstyrene, chlorostyrene, or the like), or a styrene macromerhaving a polystyrene structural unit.

The other copolymerizable monomer in the self-dispersing polymer may beused individually, or in combination of two or more types.

When the self-dispersing polymer includes the other constituent unit,the content is preferably from 10% by mass to 80% by mass, morepreferably from 15% by mass to 75% by mass, and particularly preferablyfrom 20% by mass to 70% by mass. When two or more types of the monomerforming the other constituent unit are used in combination, the totalcontent is preferably in the range mentioned above.

The self-dispersing polymer according to the exemplary embodiment of theinvention is preferably a polymer obtainable by polymerizing at leastthree types of an alicyclic (meth)acrylate, another copolymerizablemonomer and a hydrophilic group-containing monomer, and more preferablya polymer obtainable by polymerizing at least three types of analicyclic (meth)acrylate, an alkyl group-containing (meth)acrylatehaving a linear or branched chain having 1 to 8 carbon atoms, and ahydrophilic group-containing monomer, from the viewpoint of dispersionstability.

According to the exemplary embodiment of the invention, it is preferablethat the content of the (meth)acrylate having a linear or branched alkylgroup having 9 or more carbon atoms, and the constituent unit having asubstituent with high hydrophobicity, which is derived from an aromaticgroup-containing macromonomer or the like, is substantially none, and itis more preferable that the polymer does not include any of theconstituent units at all, from the viewpoint of dispersion stability.

The self-dispersing polymer according to the exemplary embodiment of theinvention may be a random copolymer having the respective constituentunits introduced irregularly, or may be a block copolymer having therespective constituent units introduced regularly. If the first polymeris a block copolymer, the respective constituent units may besynthesized in a certain order of introduction, or the same constituentcomponent may be used two or more times. However, it is preferable thatthe first polymer is a random copolymer, from the viewpoints ofall-purpose usability and manufacturability.

The range of molecular weight of the self-dispersing polymer accordingto the exemplary embodiment of the invention is preferably from 3000 to200,000, more preferably from 10,000 to 200,000, and further preferablyfrom 30,000 to 150,000, in terms of weight average molecular weight.When the weight average molecular weight is 3,000 or more, the amount ofthe water-soluble component can be effectively suppressed. When theweight average molecular weight is 200,000 or less, the self-dispersionstability can be enhanced.

Here, the weight average molecular weight can be measured by gelpermeation chromatography (GPC).

From the viewpoint of controlling the hydrophilicity and hydrophobicityof the polymer, the self-dispersing polymer according to the exemplaryembodiment of the invention is preferably a vinyl polymer which includesa structure derived from an alicyclic (meth)acrylate at acopolymerization ratio of 20% by mass to 90% by mass, and at least oneof a structure derived from a dissociative group-containing monomer anda structure derived from a (meth)acrylate containing a chain-like alkylgroup having 1 to 8 carbon atoms, and has an acid value of from 20 to120, a total content of the hydrophilic structural units of 25% by massor less, and a weight average molecular weight of from 3,000 to 200,000.

The first polymer is more preferably a vinyl polymer which includes astructure derived from a bicyclic (meth)acrylate or a polycyclic(meth)acrylate having three or more rings at a copolymerization ratio of20% by mass or more and less than 90% by mass, and a structure derivedfrom a (meth)acrylate containing a chain-like alkyl group having 1 to 4carbon atoms at a copolymerization ratio of 10% by mass or more and lessthan 80% by mass, and a structure derived from a carboxygroup-containing monomer at an acid value in the range of 25 to 100, andhas a total content of the hydrophilic structural unit of 25% by mass orless, and a weight average molecular weight of from 10,000 to 200,000.

Furthermore, the first polymer is particularly preferably a vinylpolymer which includes a structure derived from a bicyclic(meth)acrylate or a polycyclic (meth)acrylate having three or more ringsat a copolymerization ratio of 40% by mass or more and less than 80% bymass, and at least a structure derived from methyl (meth)acrylate orethyl (meth)acrylate at a copolymerization ratio of 20% by mass or moreand less than 60% by mass, and a structure derived from acrylic acid ormethacrylic acid at an acid value in the range of 30 to 80, and has atotal content of the hydrophilic structural unit of 25% by mass or less,and a weight average molecular weight of from 30,000 to 150,000.

In embodiments of the invention, the glass transition temperature of theself-dispersible polymer is not particularly limited, but is preferably150° C. to 250° C., and is more preferably 160° C. to 200° C. from theviewpoints of the block resistance and the abrasion resistance of theimage.

When the glass transition temperature of the self-dispersing polymer is150° C. or higher, the blocking resistance (particularly, under the hightemperature and high humidity conditions) may be improved. When theglass transition temperature is 250° C. or lower, the abrasionresistance of the image is enhanced.

The glass transition temperature of the self-dispersing polymer can beappropriately controlled according to methods conventionally used. Forexample, the glass transition temperature of the self-dispersing polymercan be controlled to a desired range by appropriately selecting the typeof the polymerizable group of the monomer constituting theself-dispersing polymer, the type or the composition ratio of thesubstituent on the monomer, the molecular weight of the polymermolecule, or the like.

For the glass transition temperature (Tg) of the self-dispersing polymeraccording to the exemplary embodiment of the invention, a measured Tgthat is obtainable by actual measurement is applied. Specifically, themeasured Tg means a value measured under conventional measurementconditions using a differential scanning calorimeter (DSC) EXSTAR6220(trade name) manufactured by SII Nanotechnology, Inc.

However, if measurement is difficult due to degradation of the polymeror the like, a calculated Tg that is computed by the followingcalculation formula, is applied.

The calculated Tg is calculated by the following formula (1):1/Tg=Σ(X_(i)/Tg_(i))  (1)

Here, it is assumed that in the polymer serving as the object ofcalculation, n species of monomer components, with i being from 1 to n,are copolymerized. X, is the weight fraction of the i^(th) monomer(ΣX_(i)=1), and Tg_(i) is the glass transition temperature (absolutetemperature) of a homopolymer of the i^(th) monomer, provided that Etakes the sum of i=1 to i=n. Furthermore, for the value of the glasstransition temperature of a homopolymer of each monomer (Tg_(i)), thevalues given in Polymer Handbook (3^(rd) edition) (J. Brandrup, E. H.Immergut, (Wiley-Interscience, 1989)) are employed.

The I/O value of the self-dispersing polymer is not particularlylimited, but from the viewpoints of blocking resistance and thestability of the ink composition, the value is preferably from 0.20 to0.55, more preferably from 0.30 to 0.54, and even more preferably from0.40 to 0.50.

If the I/O value of the self-dispersing polymer is less than 0.20, thestability of the ink composition may be decreased. If the I/O value isgreater than 0.55, blocking resistance (particularly, under hightemperature and high humidity conditions) may be decreased.

The I/O value, which is also called as an inorganicity value/organicityvalue, is a value that deals with the polarity of various organiccompounds in an organic conceptual manner, and is one of functionalgroup contribution methods setting parameters to each functional group.

The I/O value is explained in detail in “Organic Conceptual Diagram” (byKoda Yoshio, published by Sankyo Publishing Co., Ltd. (1984) and thelike. The concept of the I/O value is to indicate the result of dividingthe properties of a compound into organic groups representing covalentbonding properties and inorganic groups representing ion bondingproperties, and rating every organic compound as a point on a Cartesiancoordinate system designated as an organic axis and an inorganic axis.

The inorganicity value is a value obtained by evaluating the magnitudeof the influence of various substituents or bonds carried by an organiccompound on the boiling point, and converting the magnitude into anumerical data based on the hydroxyl group. Specifically, when thedistance between the boiling point curve of a linear alcohol and theboiling point curve of a linear paraffin is taken in the vicinity of acompound of five carbon atoms, the result is about 100° C. Thus, theinfluence of one hydroxyl group is defined as 100 as a numerical value,and the value obtained by converting the influence of varioussubstituents or various bonds on the boiling point into a numericalvalue based on this value of 100, serves as the inorganicity value ofthe substituent carried by an organic compound. For example, theinorganicity value of a —COOH group is 150, and the inorganicity valueof a double bond is 2. Therefore, the inorganicity value of an organiccompound of a certain type means the sum of the inorganicity values ofvarious substituents, bonds and the like carried by the compound.

The organicity value is defined by taking a methylene group in themolecule as a unit, and defining the influence of a carbon atomrepresenting the methylene group on the boiling point as the reference.That is, when one carbon atom is added to a linear saturated hydrocarboncompound having around 5 to 10 carbon atoms, the average value of anincrease in the boiling point is 20° C. Thus, the organicity value ofone carbon atom is defined as 20 based on this value, and the value ofconverting the influence of various substituents or bonds on the boilingpoint based on this value of 20, serves as the organicity value. Forexample, the organicity value of a nitro group (—NO₂) is 70.

An I/O value approximating to zero represents that the organic compoundis non-polar (hydrophobic, high organicity), and a larger valuerepresents that the organic compound is polar (hydrophilic, highinorganicity).

According to the present invention, the I/O value of the self-dispersingpolymer means a value determined by the following method. The I/O value(=I value/O value) of each monomer constituting the self-dispersingpolymer is calculated based on the organicity (O value) and theinorganicity (I value) described in Koda Yoshio, “Organic ConceptualDiagram—Fundamentals and Applications” (1984), p. 13. For each of themonomers constituting the polymer, a product of the (I/O value) and (mol% in the polymer) was calculated, these products were summed, and thevalue obtained by rounding off at the third decimal place was defined asthe I/O value of the self-dispersing polymer.

As the method of calculating the inorganicity value of each monomer,generally a double bond is regarded as having an inorganicity of 2 uponaddition; however, since the double bond disappears afterpolymerization, a value that does not add the portion of double bond asthe inorganicity value of the monomers was used to calculate the I/Ovalue of the self-dispersing polymer used in the present invention.

According to the exemplary embodiment of the invention, a polymer havinga desired I/O value can be constructed by appropriately adjusting thestructure and content of the monomers constituting the self-dispersingpolymer.

Hereinafter, specific examples of the self-dispersing polymer will belisted as exemplary compounds, but the present invention is not limitedto these. The numbers in the parentheses represent the mass ratio of thecopolymerized components.

Methyl methacrylate/isobornyl methacrylate/methacrylic acid copolymer(20/72/8), glass transition temperature: 180° C., I/O value: 0.44

Methyl methacrylate/isobornyl methacrylate/methacrylic acid copolymer(40/52/8), glass transition temperature: 160° C., I/O value: 0.50

Methyl methacrylate/isobornyl methacrylate/dicyclopentanylmethacrylate/methacrylic acid copolymer (20/62/10/8), glass transitiontemperature: 170° C., I/O value: 0.44

Methyl methacrylate/dicyclopentanyl methacrylate/methacrylic acidcopolymer (20/72/8), glass transition temperature: 160° C., I/O value:0.47

For the calculation of the I/O value, the following values were used asthe I/O values of the monomers constituting the polymer.

Methyl methacrylate: 0.60, isobornyl methacrylate: 0.29, dicyclopentanylmethacrylate: 0.32, methacrylic acid 0.47

The method for producing a self-dispersing polymer according to theexemplary embodiment of the invention is not particularly limited, andthe polymer can be produced by copolymerizing a monomer mixtureaccording to a known polymerization method. Among such polymerizationmethods, it is more preferable to perform polymerization in an organicmedium from the viewpoint of droplet ejection properties when formedinto an ink composition, and a solution polymerization method isparticularly preferable.

In regard to the method for producing the self-dispersing polymer of theexemplary embodiment of the invention, the water-insoluble polymer asdescribed above can be produced by subjecting a mixture including amonomer mixture and if necessary, an organic solvent and a radicalpolymerization initiator, to a copolymerization reaction under an inertgas atmosphere.

The method for producing an aqueous dispersion of self-dispersingpolymer particles according to the exemplary embodiment of the inventionis not particularly limited, and an aqueous dispersion ofself-dispersing polymer particles can be obtained by a known method. Theprocess of obtaining a self-dispersing polymer as an aqueous dispersionis preferably a phase inversion emulsification method including thefollowing process (1) and process (2).

Process (1): a process of obtaining a dispersion by stirring a mixturecontaining a water-insoluble polymer, an organic solvent, a neutralizingagent and an aqueous medium.

Process (2): a process of removing at least a portion of the organicsolvent from the dispersion.

The process (1) is preferably a treatment of first dissolving thewater-insoluble polymer in an organic solvent, slowly adding aneutralizing agent and an aqueous medium thereto, and mixing andstirring the mixture to obtain a dispersion. As such, when aneutralizing agent and an aqueous medium are added into a solution ofthe water-insoluble polymer dissolved in an organic solvent, aself-dispersing polymer particle having a particle size with higherstorage stability can be obtained without requiring a strong shearforce.

The method of stirring the mixture is not particularly limited, and anygenerally used mixing and stirring apparatus, or if necessary, adispersing machine such as an ultrasonic dispersing machine or a highpressure homogenizer can be used.

Preferable examples of the organic solvent include alcohol-basedsolvents, ketone-based solvents, and ether-based solvents.

Examples of the alcohol-based solvents include isopropyl alcohol,n-butanol, t-butanol, ethanol and the like. Examples of the ketone-basedsolvents include acetone, methyl ethyl ketone, diethyl ketone, methylisobutyl ketone, and the like. Examples of the ether-based solventsinclude dibutyl ether, dioxane, and the like. Among these organicsolvents, ketone-based solvents such as methyl ethyl ketone andalcohol-based solvents such as isopropyl alcohol are preferred.

It is also preferable to use isopropyl alcohol and methyl ethyl ketonein combination. When the solvents are used in combination,aggregation/precipitation or fusion between particles does not occur,and a self-dispersing polymer particle having a microparticle size withhigh dispersion stability can be obtained. This is thought to be becausethe polarity change upon phase inversion from an oil system to anaqueous system becomes mild.

The neutralizing agent is used to partially or entirely neutralize thedissociative groups so that the self-dispersing polymer can form astable emulsified or dispersed state in water. In the case where theself-dispersing polymer of the exemplary embodiment of the invention hasan anionic dissociative group as the dissociative group, examples of theneutralizing agent to be used include basic compounds such as organicamine compounds, ammonia, and alkali metal hydroxides. Examples of theorganic amine compounds include monomethylamine, dimethylamine,trimethylamine, monoethylamine, diethylamine, triethylamine,monopropylamine, dipropylamine, monoethanolamine, diethanolamine,triethanolamine, N,N-dimethyl-ethanolamine, N,N-diethyl-ethanolamine,2-diethylamino-2-methyl-1-propanol, 2-amino-2-methyl-1-propanol,N-methyldiethanolamine, N-ethyldiethanolamine, monoisopropanolamine,diisopropanolamine, and triisopropanolamine, etc. Examples of the alkalimetal hydroxide include lithium hydroxide, sodium hydroxide andpotassium hydroxide. Among them, sodium hydroxide, potassium hydroxide,triethylamine, and triethanolamine are preferred from the viewpoint ofthe stabilization of dispersion of the self-dispersing polymer particlesof the exemplary embodiment of the invention into water.

These basic compounds are preferably used in an amount of from 5 mol %to 120 mol %, more preferably from 20 mol % to 100 mol %, and furtherpreferably from 30 mol % to 80 mol %, based on 100 mol % of thedissociative group. When the content is 15 mol % or more, an effect ofstabilizing the dispersion of particles in water is exhibited, and whenthe content is 80 mol % or less, an effect of reducing water-solublecomponents is obtained.

In the process (2), an aqueous dispersion of self-dispersing polymerparticles can be obtained by distilling off the organic solvent from thedispersion obtained in the process (1) by a conventional method such asdistillation under reduced pressure, to thereby bring about phaseinversion into an aqueous system. The organic solvent in the obtainedaqueous dispersion is substantially removed, and the amount of theorganic solvent is preferably 0.2% by mass or less, and more preferably0.1% by mass or less.

The average particle size of the self-dispersing polymer particlesaccording to the exemplary embodiment of the invention is preferably inthe range of 1 nm to 100 nm, more preferably 3 nm to 80 nm, and furtherpreferably 5 nm to 60 nm. The average particle size is particularlypreferably from 5 nm to 40 nm. With an average particle size of 1 nm ormore, manufacturability is enhanced. Further, with an average particlesize of 100 nm or less, storage stability is enhanced. Here, the averageparticle size means a volume average particle size.

The particle size distribution of the self-dispersing polymer particlesis not particularly limited, and the polymer particles may have a broadparticle size distribution or a mono-dispersed particle sizedistribution. Water-insoluble particles may also be used as mixtures oftwo or more types.

The average particle size and particle size distribution of theself-dispersing polymer particles can be measured using, for example, alight scattering method.

In the ink composition of the exemplary embodiment of the invention, theself-dispersing polymer particles preferably exist in a form that doesnot substantially contain a colorant.

The self-dispersing polymer particles of the exemplary embodiment of theinvention have excellent self-dispersibility, and the stability of adispersion of the polymer alone is very high. However, for example,since the function as a so-called dispersant for stably dispersing apigment is not very significant, if the self-dispersing polymeraccording to the exemplary embodiment of the invention is present in theink composition in a form containing a pigment, consequently thestability of the ink composition as a whole may be greatly decreased.

The ink composition of the present invention may contain one type ofself-dispersing polymer particles alone, or may contain two or moretypes of such particles.

The content of the self-dispersing polymer particles in the inkcomposition of the exemplary embodiment of the invention is preferablyfrom 1% by mass to 30% by mass, more preferably from 2% by mass to 20%by mass, and particularly preferably from 2% by mass to 10% by mass,based on the ink composition for inkjet recording, from the viewpoint ofthe glossiness of the image.

The content ratio of the coloring particles and the self-dispersingpolymer particles (coloring particles/self-dispersing polymer particles)in the ink composition of the exemplary embodiment of the invention ispreferably from 1/0.5 to 1/10, and more preferably from 1/1 to 1/4, fromthe viewpoint of abrasion resistance of the image.

(Other Additives)

The ink composition of the exemplary embodiment of the invention canfurther include other additives if necessary, in addition to thecomponents mentioned above.

Examples of the other additives according to the exemplary embodiment ofthe invention include known additives such as color fading inhibitor,emulsion stabilizer, permeation accelerator, ultraviolet absorber,preservative, mildew-proofing agent, pH adjusting agent, surface tensionregulator, defoamer, viscosity adjusting agent, dispersant, dispersedstabilizer, anti-rust agent and chelating agent. These various additivesmay be added directly after the preparation of the ink composition, ormay be added during the preparation of the ink composition.Specifically, the other additives and the like described in paragraphs[0153] to [0162] of JP-A No. 2007-100071 are included.

The surface tension adjusting agent may be a nonionic surfactant, acationic surfactant, an anionic surfactant, a betaine surfactant or thelike.

The amount of addition of the surface tension adjusting agent ispreferably an amount of addition that adjusts the surface tension of theink composition to 20 mN/m to 60 mN/m, more preferably an amount ofaddition that adjusts the surface tension to 20 mN/m to 45 mN/m, andfurther preferably an amount of addition that adjusts the surfacetension to 25 mN/m to 40 mN/m, in order to spot the ink compositionsatisfactorily by the inkjet method. The surface tension of the inkcomposition can be measured, for example, using a plate method at 25° C.

Specific examples of the surfactant as a hydrocarbon type preferablyinclude anionic surfactants such as fatty acid salts, alkyl sulfuricacid ester salts, alkyl benzenesulfonates, alkyl naphthalenesulfonates,dialkyl sulfosuccinates, alkyl phosphoric acid ester salts,naphthalenesulfonic acid-formalin condensates and polyoxyethylene alkylsulfuric acid salts; and nonionic surfactants such as polyoxyethylenealkyl ether, polyoxyethylene alkyl allyl ether, polyoxyethylene fattyacid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fattyacid ester, polyoxyethylene alkyl amine, glycerin fatty acid ester andoxyethylene oxypropylene block copolymer. SURFYNOLS (trade name,products of Air Products & Chemicals) and OLFINE E1010 (trade name,surfactant, manufactured by Nisshin Chemical Industry Co., Ltd.) whichare an acetylene type polyoxyethylene oxide surfactant) are preferablyused. Furthermore, amine oxide type amphoteric surfactants such asN,N-dimethyl-N-alkyl amine oxide are preferred.

Additionally, materials described on pages (37) to (38) of JP-A No.59-157636 and Research Disclosure No. 308119 (1989) as surfactants canbe used.

When fluorocarbon (alkyl fluoride type) surfactants, siliconesurfactants or the like, such as those described in JP-A Nos.2003-322926, 2004-325707 and 2004-309806 are used, abrasion resistancecan be improved.

The surface tension regulator can be used as an antifoamer, and fluorinecompounds, silicone compounds, chelating agents represented by EDTA, andthe like can be used.

When the application of ink is carried out by the inkjet method, theviscosity of the ink composition of the exemplary embodiment of theinvention is preferably in the range of 1 mPa·s to 30 mPa·s, morepreferably in the range of 1 mPa·s to 20 mPa·s, further preferably inthe range of 2 mPa·s to 15 mPa·s, and particularly preferably in therange of 2 mPa·s to 10 mPa·s, from the viewpoints of the dropletejection stability and rate of aggregation.

The viscosity of the ink composition can be measured by, for example,Brookfield Viscometer at 20° C.

In the exemplary embodiment of the invention, the pH of the inkcomposition is preferably 7.5 to 10, and more preferably 8.0 to 9.5,from the viewpoints of the ink stability and rate of aggregation. The pHof the ink composition may be measured using a conventional pHmeasurement apparatus (for example, HM-30R; trade name, manufactured byDKK-TOA CORPORATION) at a temperature of 25° C. The pH of the inkcomposition is appropriately controlled by applying an acidic compoundor basic compound. A conventional acidic compound or basic compound maybe used as the acidic compound or basic compound without anyrestriction.

In an image forming method according to the exemplary embodiment of theinvention, an exemplary embodiment of forming an image by using an inkset of the invention which includes at least one of the inkcompositions, and at least one treatment liquid configured to formaggregates when contacted with the ink composition, is preferable.

The ink set can be used in the form of an ink cartridge holding theseinks collectively or independently, and is preferable in view of theease of handling. The ink cartridge constituted to include the ink setis known in the related technical field, and can be prepared as an inkcartridge by appropriately using a known method.

(Treatment Liquid)

The treatment liquid in the exemplary embodiment of the invention is anaqueous composition which forms an aggregate when contacted with the inkcomposition for inkjet recording, and specifically, contains at least anaggregating component which may aggregate the dispersed particles suchas the coloring particles (pigments) in the ink composition to form anaggregate and, if necessary, may contain other components. By using thetreatment liquid together with the ink composition, inkjet recording maybe speeded up and, even when high speed recording is performed, an imagehaving high density and high resolution is obtained.

The treatment liquid contains at least one aggregating component whichforms an aggregate when contacted with the ink composition. By mixingthe treatment liquid into the ink composition ejected by an inkjetmethod, aggregation of a pigment or the like which has been stablydispersed in the ink composition is promoted.

Examples of the treatment liquid include a liquid composition which maygenerate an aggregate by changing the pH of the ink composition.Thereupon, the pH (25° C.) of the treatment liquid is preferably from 1to 6, more preferably from 1.2 to 5, and further preferably from 1.5 to4 from the viewpoints of the aggregation rate of the ink composition. Inthis case, the pH (25° C.) of the ink composition used in the ejectionstep is preferably 7.5 to 9.5 (more preferably 8.0 to 9.0).

In embodiments, it is preferable that the pH (25° C.) of the inkcomposition is 7.5 or higher, and the pH (25° C.) of the treatmentliquid is 3 to 5, from the viewpoint of the image density, theresolution, and speeding-up of inkjet recording.

The aggregating component may be used alone, or two or more of them maybe used by mixing them.

The treatment liquid may be prepared by using at least one acidiccompound as the aggregating component. As the acidic compound, compoundshaving a phosphoric acid group, a phosphonic acid group, a phosphinicacid group, a sulfuric acid group, a sulfonic acid group, a sulfinicacid group, or a carboxy group, or salts thereof (e.g. polyvalent metalsalts) may be used. Among them, from the viewpoint of the aggregationrate of the ink composition, compounds having a phosphoric acid group ora carboxy group are more preferable, and compounds having a carboxygroup are further preferable.

The compound having a carboxy group is preferably selected frompolyacrylic acid, acetic acid, glycoric acid, malonic acid, malic acid,maleic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid,citric acid, tartaric acid, lactic acid, sulfonic acid, orthophosphoricacid, pyrrolidone carboxylic acid, pyrone carboxylic acid, pyrolecarboxylic acid, furan carboxylic acid, pyridine carboxylic acid,coumalic acid, thiophene carboxylic acid, nicotinic acid, or derivativesof such compound or salts thereof (for example, polyvalent metal salts,etc.) One of these compounds may be used alone or two or more of thesecompounds may be used together.

The treatment liquid in the exemplary embodiment of the invention mayfurther include an aqueous solvent (for example, water) in addition tothe acidic compound described above.

The content of the acidic compound in the treatment liquid is,preferably, from 5% by mass to 95% by mass and, more preferably, from10% by mass to 80% by mass based on the entire mass of the treatmentliquid from the viewpoint of aggregation effect.

Preferred examples of the treatment liquid that may improve the highspeed aggregation property include a treatment liquid including apolyvalent metal salt or a polyallyl amine. Examples of the polyvalentmetal salt and a polyallyl amine include salts of alkaline earth metalsbelonging to group 2 of the periodic table (for example, magnesium andcalcium), salts of a transition metal belonging to group 3 of theperiodic table (for example, lanthanum), salts of a cation of a metalbelonging to group 13 of the periodic table (for example, aluminum),salts of a lanthanide (for example, neodium), polyallylamine andpolyallylamine derivatives. As the metal salts, carboxylic acid salts(such as, salts of formic acid, salts of acetic acid, and salts ofbenzoic acid), nitric acid salts, chlorides, and thiocyanic acid saltsare preferred, and calcium salts or magnesium salt of a carboxylic acid(such as salts of formic acid, salts of acetic acid, and salts ofbenzoic acid), calcium salt of nitric acid or magnesium salt of nitricacid, calcium chloride, magnesium chloride, and calcium salt ofthiocyanic acid or magnesium salt of thiocyanic acid are more preferred.

The content of the metal salt in the treatment liquid is preferably from1% by mass to 10% by mass, more preferably, from 1.5% by mass to 7% bymass and, further preferably, from 2% by mass to 6% by mass.

The viscosity of the treatment liquid is, preferably, in a range from 1mPa·s to 30 mPa·s, more preferably, in a range from 1 mPa·s to 20 mPa·s,further preferably, in a range from 2 mPa·s to 15 mPa·s, and,particularly preferably, in a range from 2 mPa·s to 10 mPa·s from theviewpoint of the aggregation rate of the ink composition. The viscosityis measured by using VISCOMETER TV-22 (trade name, manufactured by TOKISANGYO CO., LTD.) under the condition at 20° C.

The surface tension of the treatment liquid is, preferably, from 20 mN/mto 60 mN/m, more preferably, from 20 mN/m to 45 mN/m and, furtherpreferably, from 25 mN/m to 40 mN/m from the viewpoint of theaggregation rate of the ink composition. The surface tension is measuredby using Automatic Surface Tensiometer CBVP-Z (trade name, manufacturedby Kyowa Interface Science Co. Ltd.) under the condition of being at 25°C.

EXAMPLES

Hereinafter, the present invention will be specifically described withrespect to Examples, but the present invention is not limited to theseExamples unless exceeds the subject matter of the invention. Unlessstated otherwise, the “parts” and “%” are based on mass.

The weight average molecular weight was measured by using a gelpermeation chromatography (GPC). HLC-8220 GPC (trade name, manufacturedby Tosoh Corp.) was used for the GPC, and TSKgeL SuperHZM-H, TSKgeLSuperHZ4000, and TSKgeL SuperHZ2000 (trade names, all manufactured byTosoh Corp.) were used as the columns and were connected in a series ofthree. The eluent liquid was THF (tetrahydrofuran). For the conditions,the sample concentration was 0.35% by mass, the flow rate was 0.35ml/min, the amount of sample injection was 10 μl, the measurementtemperature was 40° C., and an RI detector was used. A calibration curvewas produced from 8 samples of the 2 standard sample TSK standard,polystyrene”: “F-40”, “F-20”, “F-4”, “F-1”, “A-5000”, “A-2500”, “A-1000”and “n-propylbenzene” (trade names) manufactured by Tosoh Corp.

Example 1 Preparation of Ink Composition>

—Synthesis of Resin Dispersant P-1—

88 g of methyl ethyl ketone was added to a 1000-mL three-necked flaskequipped with an agitator and a cooling tube, and was heated to 72° C.under a nitrogen atmosphere. To this, a solution of 0.85 g ofdimethyl-2,2′-azobisisobutyrate, 50 g of phenoxyethyl methacrylate, 11 gof methacrylic acid and 39 g of methyl methacrylate dissolved in 50 g ofmethyl ethyl ketone was added dropwise over 3 hours. After the additionwas completed, the mixture was reacted for one more hour, and then asolution of 0.42 g of dimethyl-2,2′-azobisisobutyrate dissolved in 2 gof methyl ethyl ketone was added. The temperature was raised to 78° C.,and the mixture was heated for 4 hours. Methyl ethyl ketone (MEK) wasadded to the obtained reaction solution to obtain 36.8% MEK solution ofa phenoxyethyl methacrylate/methyl methacrylate/methacrylic acidcopolymer (copolymerization ratio by mass percent=50/39/11) (resindispersant P-1).

The composition of the obtained resin dispersant P-1 was confirmed by¹H-NMR, and the weight average molecular weight (Mw) determined by GPCwas 49,400. The acid value of the copolymer was determined by the methoddescribed in JIS Standards (JIS K0070: 1992), and the value was 71.7mgKOH/g. The measured Tg of the copolymer (resin dispersant P-1) was 94°C.

—Synthesis of resin dispersant P-2—

240 g of methyl ethyl ketone, 30 g of a mixture ofN-(4-vinylbenzyl)-10H-acridin-9-one andN-(3-vinylbenzyl)-10H-acridin-9-one (mixture mass ratio 1 to 1), 20 g ofmethacrylic acid and 150 g of ethyl methacrylate were added to a 1000-mLthree-necked flask equipped with an agitator and a cooling tube, andheated to 75° C. under a nitrogen atmosphere. To this, a solution of2.44 g of dimethyl-2,2′-azobisisobutyrate dissolved in 16 g of methylethyl ketone, was added. The mixture was reacted with stirring whilemaintaining the temperature of 75° C. for two hours, followed by anaddition of a solution of 1.0 g of dimethyl-2,2′-azobisisobutyratedissolved in 2.0 g of methyl ethyl ketone and further reaction for twohours. To the mixture, a solution of 1.0 g ofdimethyl-2,2′-azobisisobutyrate dissolved in 2.0 g of methyl ethylketone was added. The temperature of the mixture was raised to 80° C.,and the mixture was heated for 4 hours. Methyl ethyl ketone (MEK) wasadded to the obtained reaction solution to obtain MEK solution of amixture of N-(4-vinylbenzyl)-10H-acridin-9-one andN-(3-vinylbenzyl)-10H-acridin-9-one (mixture mass ratio 1 to 1)/ethylmethacrylate/methacrylic acid copolymer (copolymerization ratio by masspercent=15/75/10) (resin dispersant P-2).

The measured Tg of the copolymer (resin dispersant P-2) was 124° C. Acontent of a non-volatile component in the obtain MEK solution of thecopolymer (resin dispersant P-2) was measured by weighing after drying apart of the obtain MEK solution by heating under reduced pressure. Thevalue was 36.8% by weight. The composition of the obtained resindispersant P-2 was confirmed by ¹H-NMR, and the weight average molecularweight (Mw) determined by GPC was 44,200. The acid value of thecopolymer was determined by the method described in JIS Standards (JISK0070: 1992), and the value was 65.2 mgKOH/g.

—Production of Self-Dispersing Polymer Particles B-01—

560.0 g of methyl ethyl ketone was introduced into a two litterthree-necked flask equipped with an agitator, a thermometer, a refluxcooling tube and a nitrogen gas inlet tube, and the temperature wasincreased to 87° C. under a nitrogen atmosphere. While maintaining acondition of reflux in the reaction vessel (until finishing thereaction), a mixed solution formed from 220.4 g of methyl methacrylate(MMA), 301.6 g of isobornyl methacrylate (IBOMA), 58.0 g of methacrylicacid (MAA), 108 g of methyl ethyl ketone and 2.32 g of “V-601” (tradename, manufactured by Wako Pure Chemical Industries, Ltd.) was addeddropwise at a constant rate so that dropping would be completed in 2hours. After stirring the reaction mixture for one hour after theaddition was completed, a solution formed from 1.16 g of “V-601” and 6.4g of methyl ethyl ketone was added, and the mixture was stirred for 2hours (referred as a reaction step (1)). The reaction step (1) wasrepeated four times and then a solution formed from 1.16 g of “V-601”and 6.4 g of methyl ethyl ketone was further added, and the mixture wasstirred for 3 hours. The temperature was lowered to 65° C. afterperforming the polymerization reaction, and 163 g of isopropanol wasadded. The reaction mixture was rendered to cool in the atmosphere.

The weight average molecular weight (Mw) of the obtained copolymer was63,000, and the acid value was 65.1 (mg KOH/g).

Next, 317.3 g of the polymerized solution (solid content 41.0%) wasweighed, and 46.4 g of isopropanol, 1.65 g of a 20% aqueous solution ofmaleic anhydride (which is correspond to 0.3% by weight as maleic acidto the amount of the copolymer) and 40.77 g of a 2 mol/L aqueous NaOHsolution were added. The temperature in the reaction vessel wasincreased to 70° C. Subsequently, 380 g of distilled water was addeddropwise at a rate of 10 mL/min to achieve dispersion in water(dispersion step). Subsequently, 287.0 g of the solvent includingisopropanol, methyl ethyl ketone and water was distilled off under thereduced pressure, while holding for 1.5 hours at a temperature of 70° C.in the reactive vessel (solvent removing step). Then, 0.278 g of PROXELGXL(S) (trade name, manufactured by Arch Chemicals Japan Inc.) (whichcorresponds 440 ppm as benzoisothiazoline to a solid of the copolymer)was added. Then the resulting liquid was filtered with a filter having apore diameter of 1 μm to obtain a dispersion of a self-dispersingpolymer particle (B-01) at a solids concentration of 26.5%. The obtainedself-dispersing polymer particle was diluted with ion exchanged water toobtain aqueous dispersion of 25.0% concentration for measurement ofphysical properties. The obtained values for the physical propertieswere followings. a pH; 7.8, electric(al) conductivity; 461 mS/m,viscosity; 14.8 mPa·s, and volume average particle diameter; 2.8 nm.

<Measurement of Glass Transition Temperature Tg>

The glass transition temperature of the obtained polymer (particlesB-01) was measured by the following method, and was 160° C.

The polymer solution after polymerization in an amount of 0.5 g in termsof solid fraction was dried under reduced pressure at 50° C. for 4 hoursto obtain a polymer solid fraction. The obtained polymer solid fractionwas used to measure Tg by a differential scanning calorimeter (DSC)EXSTAR6220 (trade name) manufactured by SII Nanotechnology, Inc. Themeasurement conditions were such that 5 mg of a sample was sealed in analuminum pan, and the value of the peak top of DDSC from the measurementdata obtained at the time of second temperature increase in thefollowing temperature profile under a nitrogen atmosphere, wasdesignated as Tg.

from 30° C. to −50° C. (cooled at 50° C./min)

from −50° C. to 120° C. (heated at 20° C./min)

from 120° C. to −50° C. (cooled at 50° C./min)

from −50° C. to 120° C. (heated at 20° C./min)

<Measurement of Volume Average Particle Diameter (Mv)>

An aqueous dispersion of the resultant self-dispersible polymer particlewas arbitrarily diluted to the concentration (loading index of the rangeof 0.1 to 10) suitable for measurement, the volume average particlediameter of all aqueous dispersions was measured under same measurementconditions by a dynamic light scattering method, using an ULTRA FINEPARTICLE DIAMETER DISTRIBUTION MEASURER NANOTRACK UPA-EX150 (trade name,manufactured by Nikkiso Co., Ltd.). That is to say, it was measuredunder the following conditions: particle permeability of transmission,particle refractive index of 1.51, particle shape of nonsphere, densityof 1.2 g/cm³, water as the solvent, cell temperature of 18° C. to 25° C.

˜Production of Dispersion of Resin-Coated Pigment Particle˜

(Production of Cyan Pigment Dispersion C)

100 g of Pigment Blue 15:3 (phthalocyanine blue A 220 wet cake (pigmentsolid content 33.5%), made from Dainichiseika Color & Chemicals Mfg.Co., Ltd.) as pigment solid content, 45 g of the phenoxy ethylmethacrylate/methyl methacrylate/methacrylic acid copolymer (resindispersant P-1) as the solid content, 140 g of methyl ethyl ketone, 50.6g of 1 mol/L aqueous sodium hydroxide solution (degree of neutralizationwith respect to the methacrylic acid: 88 mol %) as a pH adjuster, 331 gof ion exchanged water is dispersed with disperser in advance as apigment, a further eight-pass process was performed by a disperser(trade name; MICROFLUIDIZER M-140K, manufactured by Microfluidic™Corporation, 150 MPa).

Subsequently, methyl ethyl ketone in the resultant dispersion wasremoved under reduced pressure at 56° C., a further 1 part of water wasremoved, a centrifugal treatment was performed at 8,000 rpm for 30minutes by a 50 mL centrifugal tube, using HIGH SPEED CENTRIFUGAL COOLER7550 (trade name, manufactured by Hisamitsu Pharmaceutical Co., Inc.),the supernatant solution, other than the precipitates, was collected.

Subsequently, the resultant dispersion (supernatant liquid) was heatedto 70° C. for 4 hours, and then 80 ppm of 2-methyl-4-isothiazolin-3-on,40 ppm of 5-chloro-2-methyl-isothiazolin-3-on, 10 ppm of2-bromo-2-nitropropan-1,3-diol, 30 ppm of 4,4-dimethyloxazolidine, 80ppm of 1,2-benzisothiazolin-3-on, and 30 ppm of2-n-octyl-4-isothiazolin-3-on as an antiseptic agent were added thereto,followed by filtration, and the filtrate was collected. The pigmentconcentration was calculated from the absorption spectrum, a pigmentconcentration of 15% resin-coated pigment particle dispersion (cyanpigment dispersion C) was obtained. The dispersion was pH 8.5 andviscosity of 2.9 mPa·s.

<Measurement of Particle Diameter of Resin-Coated Pigment Particle>

With respect to the resultant resin-coated pigment particle dispersion,the volume average particle diameter was measured by a dynamic lightscattering method, using PARTICLE DIAMETER DISTRIBUTION MEASURERNANOTRACK UPA-EX150 (trade name, manufactured by Nikkiso Co., Ltd.).Measurement was performed by adding 10 mL of the ion exchange water to10 μL of the resin-coated pigment particle dispersion to produce ameasurement sample liquid, followed by adjusting the temperature to 25°C. As a measurement result, volume average particle diameter of theresin-coated pigment particle was 88 nm.

(Production of Magenta Pigment Dispersion M)

100 g of Pigment Red 122 (CROMOPHTAL JET MAGENTA DMQ; trade name,manufactured by Chiba specialty corporation; Magenta pigment), 30 g ofthe resin dispersant P-2 as the solid content, 133 g of methyl ethylketone, 27.2 g of 1 mol/L aqueous NaOH solution (degree ofneutralization with respect to the methacrylic acid: 78 mol %), and 424g of ion exchanged water were mixed, further dispersed by dispersermixing in advance, and a 10-pass process was performed by a disperser(MICROFLUIDIZER M-140K; trade name, 150 MPa).

Subsequently, the same operation as performed for the cyan pigmentdispersion C was performed to obtain a pigment concentration of 15%resin-coated pigment particle dispersion (Magenta pigment dispersion M).Further, the volume average particle diameter, pH, and viscosity of theresultant dispersion using the same method as described above weremeasured to have a diameter of 76 nm, pH 8.6, and viscosity of 2.8mPa·s.

˜Preparation of Ink˜

(Preparation of Cyan Ink)

Each component was mixed so as to have the ink composition describedbelow, using cyan pigment dispersion C as obtained above and aself-dispersible polymer particle B-01. The resultant was charged by adisposable syringe made of a plastic. The resultant was filtrated withPVDF 5 μm filter (trade name; MILLEX-SV, diameter of 25 nm, manufacturedby Millipore corporation) to produce cyan ink (ink composition forinkjet) C-01.

<Composition of Cyan Ink>

Cyan pigment (Pigment Blue 15:3) 2.5%

The resin dispersant P-1 (solid content) 1.125%

The self-dispersible polymer particle B-01 (solid content) 8.5%

Colloidal silica (solid content) 0.05%

(trade name; SNOWTEX XS, volume average particle diameter: 4 to 6 nm,manufactured by Nissan Chemical Industries, Ltd.)

SUNNIX GP 250 8%

(trade name, manufactured by Sanyo Chemical Industries, Ltd.,hydrophilic organic solvent, I/O value 1.30)

Tripropylene glycol monomethyl ether (TPGmME) 8%

(trade name; MFTG, manufactured by Nippon Nyukazai Co., Ltd.,hydrophilic organic solvent, I/O value 0.80)

Urea (manufactured by Nissan Chemical Industries, Ltd., solid wettingagent) 5%

NEWPOLE PE-108 (trade name, manufactured by Sanyo Chemical Industries,Ltd., thickening agent) 0.15%

OLFINE E1010 (trade name, manufactured by Nissin Chemical Industry Co.,Ltd., surfactant) 1%

Ion exchanged water remainder (up to the total amount of 100%)

(Preparation of Magenta Ink)

Magent ink (ink composition for inkjet) M-01 was prepared in a mannersubstantially same as that in preparation of the cyan ink C-01 exceptthat each component was mixed so as to have the ink compositiondescribed below, using the magenta pigment dispersion M as obtainedabove and a resin dispersant P-2.

<Composition of Magenta Ink>

Magenta pigment (Pigment Red 122) 5.0%

The resin dispersant P-2 (solid content) 1.5%

The self-dispersible polymer particle B-01 (solid content) 7.25%

SUNNIX GP 250 10%

(trade name, manufactured by Sanyo Chemical Industries, Ltd.,hydrophilic organic solvent, I/O value 1.30)

Tripropylene glycol monomethyl ether (TPGmME) 6%

(trade name; MFTG, manufactured by Nippon Nyukazai Co., Ltd.,hydrophilic organic solvent, I/O value 0.80)

Urea (manufactured by Nissan Chemical Industries, Ltd., solid wettingagent) 5%

NEWPOLE PE-108 (trade name, manufactured by Sanyo Chemical Industries,Ltd., thickening agent) 0.05%

OLFINE E1010 (trade name, manufactured by Nissin Chemical Industry Co.,Ltd., surfactant) 1%

Ion exchanged water remainder (up to the total amount of 100%)

Preparation of Treatment Liquid

Each component was mixed so as to have the composition described belowto prepare the treatment liquid T-1. The viscosity and surface tensionof the obtained treatment liquid was measured by the same method asdescribed above to have a viscosity of 2.3 mPa·s, surface tension of42.5 mN/m, and pH 1.0.

<Composition>

malonic acid (manufactured by Tateyama Kasei Co., Ltd.) 11.3%

DL-malic acid (manufactured by Fuso Chemical Co., Ltd.) 14.5%

Diethylene glycol monobutyl ether 4%

(trade name; BDG, manufactured by Nippon Nyukazai Co., Ltd.)

Tripropylene glycol monomethyl ether 4%

(trade name; MFTG, manufactured by Nippon Nyukazai Co., Ltd.)

Ion exchanged water 66.2%<

<Image Forming and Evaluation>

˜Image Forming˜

An Inkjet head 1 constituted as shown in FIGS. 6 to 8 and with thesilicon nozzle plate was prepared, and the magenta ink as obtained abovewas charged to the connected storage tank thereto. The silicon nozzleplate is formed of single crystal silicon, and a silicon oxide film(SiO₂ film) is formed on the surface thereof at a side toward the inkejection direction of the nozzle by a CVD method by introducing SiCl₄and water vapor to a chemical vapor deposition (CVD) reactor. Thethickness of SiO₂ film is 50 nm. Further, after performing an oxygenplasma process, chemical vapor deposition (CVD) was performed usingC₈F₁₇C₂H₄SiCl₃, and the liquid repellent film was formed on SiO₂ film.The liquid repellent film was formed by introducing C₈F₁₇C₂H₄SiCl₃ andwater vapor at the low pressure into CVD reactor. The thickness of theliquid repellent film is 10 nm. Further, plural nozzles as shown inFIGS. 2 to 4 are arranged two-dimensionally in a matrix form in thesilicon nozzle plate, and ink droplets can be ejected with highprecision as shown in FIG. 5. As a recording medium, TOKUBISHI ART BOTHFACES N (trade name, manufactured by Mitsubishi Paper Mills, Ltd.) wasprepared.

The recording medium was fixed on a transferable stage in thepredetermined straight line direction at 500 mm/second, stagetemperature was held at 30° C., the treatment liquid as obtained abovewas coated at a thickness of about 1.2 μm with a bar coater, followed bydrying at 50° C. for 2 seconds immediately after coating. The preparedinkjet head was fixed and disposed such that the line direction (w, 310,320, 330, 340 etc. in FIG. 5) where nozzle was aligned to an inclinationof 75.7° (90°-α in FIGS. 2 and 5) with respect to the direction(principal scanning direction) orthogonal to the movement direction(sub-scanning direction) of the stage. While the recording medium wasmoved at the constant speed in the sub-scanning direction, ink wasejected linearly under conditions of an ink droplet volume of 6.0 pL,ejection frequency of 25.7 kHz, resolution of 1200 dpi×1200 dpi, and animage was recorded which contained a 50% solid image with an area of 2square cm, a 4 to 8 pt image of the character of

(TODOROKI)“, and a 4 pt image of the character of

(TODOROKI)” as a white letter on a solid image.

Immediately after recording, the image was passed between a pair offixing rollers, which were dried at 60° C. for 3 seconds and at the 60°C., and fixing process was performed at a NIP pressure of 0.25 MPa and aNIP width of 4 mm to obtain an evaluation sample.

˜Image Evaluation˜

—1. Resolution of Image—

Among image of the resultant evaluation sample, the resolution wasevaluated according to evaluation criteria described below by visualobservation with respect to a 4 to 8 pt image of the character of

(TODOROKI)” and a 4 pt image of the character of

(TODOROKI)” as a white letter on a solid image. The evaluation resultsare shown in Table 2 below.

<Evaluation Criteria>

AA: Resolution is good for a 4 pt character, and the resolution is at alevel having no problems in practical application.

A: The decrease in resolution was recognized at a part of the 4 ptcharacters, but the resolution is at a level having no problems inpractical application.

B: The decrease in resolution is recognized even in characters largerthan 4 pt and the resolution was at a level having low practicality.

C: The character is lost and the decrease in resolution was prominent,and the resolution was at a level having extremely low practicality.

—2. Image Density—

The density of the image section of the obtained evaluation sample wasmeasured using Reflection Densitometer (trade name; XRITE 938,manufactured by X-rite corporation) and was evaluated by the evaluationcriteria described below. The evaluation results are shown in Table 2below.

<Evaluation Criteria>

AA: Sufficient density is obtained, and the density is of an extremelygood level.

A: Density is obtained, and the density is of a good level.

B: Practical application presents no problem at this level.

C: Density is reduced, and the density is at a level having lowpracticality.

D: Density is highly reduced and the density is at a level having verylow practicality.

—3. Ink Ejection Property—

Ejection ratio was measured by conditions below and image unevenness wasobserved visually and was evaluated using the evaluation criteria below.

(1) ejection ratio [%] after continuous ejection test for 60 minutes

(2) ejection ratio [%] after stopping for 30 minutes after ejection for1 minute

<Evaluation Criteria>

AA: (1) and (2) are 99% or more, and image unevenness is not recognizedat all.

A: (1) and (2) are 95% or more, and there are no practical issues withimage unevenness.

B: (1) and (2) are 90% or more, and image unevenness is recognized, butthere are no practical issues.

C: (1) and (2) are 80% or more, and image unevenness can be clearlyrecognized, but is of a low level causing practical problems.

D: (1) and (2) are less than 80%, image unevenness is conspicuous, andpracticality is of a very low level.

<Ejection Ratio>

Ejection ratio was calculated by Formula belowEjection ratio [%]=(number of nozzles capable of ejecting under theconditions)/(total number of nozzles)×b 100.

—4. Head Reliability—

The inkjet head was continuously ejected at 25.7 kHz for 6000 hundredmillion times, and then image is recorded, and line image of 75×2400 dpiwas drawn at an ejection frequency of 25.7 kHz using 96 nozzles. Withrespect to the line image, the center value of the line was measuredusing a DOT ANALYZER DA-6000, trade name, manufactured by Oji ScientificInstruments Co., Ltd., and a standard deviation σ of misalignment ofeach line was calculated. The evaluation results are shown in Table 2below.

<Evaluation Criteria>σ<2 μm  AA:2 μm≦σ≦3 μm  A:3 μm≦σ≦5 μm  B:5 μm≦σ<7 μm  C:7 μm≦σ  D:

—5. State of Liquid Repellent Film

The ink-jet head was continuously ejected at 25.7 kHz six hundredbillion times, and then an image was recorded, the state of the film(liquid repellent film) formed by using C₈F₁₇C₂H₄SiCl₃ around 2048nozzle holes was observed by an optical microscope, and change in thefilm formed by using C₈F₁₇C₂H₄SiCl₃ was evaluated according toevaluation criteria below. The evaluation results are shown in Table 2below.

<Evaluation Criteria>

AA: The state of the liquid repellent film around all the nozzle holesis good

A: The number of the nozzle around which the state of the liquidrepellent film is changed is less than 5

B: The number of the nozzle around which the state of the liquidrepellent film is changed is 5 or more and less than 10.

C: The number of the nozzle around which the state of the liquidrepellent film is changed is 10 or more and less than 20.

D: The number of the nozzle around which the state of the liquidrepellent film is changed is 20 or more.

Example 2

An image was recorded and evaluated in substantially the same manner asthat in Example 1, except that the amount of colloidal silica used inthe preparation of the ink in Example 1 was changed from 0.05% by massto 1% by mass with respect to the total mass of the ink composition. Theevaluation results are shown in Table 2 below.

Example 3

An image was recorded and evaluated in a manner substantially same asthat in Example 1 except that the inkjet head 1 in Example 1 wasreplaced with the inkjet head 2 of configuration which have a siliconnozzle plate but did not have a rear flow path, that is to say, aconfiguration where the common liquid chamber was disposed on the sameside as the pressure chamber. Plural nozzles were provided in thesilicon nozzle plate as shown in FIGS. 2 to 4, and ink droplets withhigh precision can be ejected as shown in FIG. 5. Further, the siliconnozzle plate was formed of single crystal silicon as similar to that inExample 1, and silicon oxide film (SiO₂ film) was formed on the surfaceof the single crystal silicon at a side toward the ink ejectiondirection of the nozzle by an oxidization treatment. Further, a filmobtained by using C₈F₁₇C₂H₄SiCl₃ was formed on the SiO₂ film. Theevaluation results are shown in Table 2 below.

Example 4

An image was recorded and evaluated in a manner substantially same asthat in Example 1 except a self-dispersible polymer particle dispersionB-01 used in ink production in Example 1 was replaced with a polymerparticle dispersion C obtained by an emulsion polymerization process asdescribed below. The evaluation results are shown in Table 2 below.

Production of Polymer Particle Dispersion C

To a 1 L three-necked flask equipped with stirrer and reflux condenserwere placed 8.1 g of PIONIN A-43s (trade name, manufactured by TakemotoOil & Fat Co., Ltd., emulsifier) and 236.0 g of distillated water,followed by heat and stirring at 70° C. under nitrogen gas flow. 6.2 gof styrene, 3.5 g of n-butyl acrylate, 0.3 g of acrylic acid, 1.0 g ofammonium persulfate, and 40 g of distillated water were added thereto,and after stirring for 30 minutes, dropwise addition was performed at asteady speed such that this dropwise addition of a monomer solutionconsisting of 117.8 g of styrene, 66.5 g of n-butyl acrylate and 5.7 gof acrylic acid completes in 2 hours. After completion of the dropwiseaddition, a water solution consisting of 0.5 g of ammonium persulfateand 20 g of distillated water was added thereto, followed by stirring at70° C. for 4 hours, and then the temperature was raised to 85° C. andwas stirred for 2 hours. A reaction solution was cooled down, andneutralization degree was neutralized to be 0.5 using 2 mol/L aqueousNaOH solution. Through successive filtration, a polymer particle BH-1dispersion was obtained represented by the structure below. The physicalproperties of the obtained polymer particle have weight-averagemolecular weight of 232,000, acid value of 23 mgKOH/g, and volumeaverage particle diameter of 70 nm.

Example 5

An image was recorded and evaluated in a manner substantially same asthat in Example 4 except that the inkjet head 1 in Example 4 wasreplaced with the inkjet head 2 of configuration which had a siliconnozzle plate but did not have a rear flow path, that is to say, aconfiguration where the common liquid chamber was disposed on the sameside as the pressure chamber. Plural nozzles were provided in thesilicon nozzle plate as shown in FIGS. 2 to 4, and ink droplets could beejected with high precision as shown in FIG. 5. Further, the siliconnozzle plate was formed of single crystal silicon as similar to that inExample 1, and silicon oxide film (SiO₂ film) was formed on the surfaceof the single crystal silicon at a side toward the ink ejectiondirection of the nozzle by an oxidization treatment. Further, a filmobtained by using C₈F₁₇C₂H₄SiCl₃ was formed on the SiO₂ film. Theevaluation results are shown in Table 2 below.

Comparative Example 1

An image was recorded and evaluated in a manner substantially same asthat in Example 1 except that colloidal silica used in the inkproduction in Example 1 was not contained. The evaluation results areshown in Table 2 below.

Comparative Example 2

An image was recorded and evaluated in a manner substantially same asthat in Comparative Example 1 except that the inkjet head 1 inComparative Example 1 was replaced with the inkjet head 2 ofconfiguration which had a silicon nozzle plate but did not have a rearflow path, that is to say, a configuration where the common liquidchamber was disposed on the same side as the pressure chamber. Pluralnozzles were provided in the silicon nozzle plate as shown in FIGS. 2 to4, and ink droplets could be ejected with high precision as shown inFIG. 5. Further, the silicon nozzle plate was formed of single crystalsilicon, as similar to that in Example 1, and silicon oxide film (SiO₂film) was formed on the surface of the single crystal silicon at a sidetoward the ink ejection direction of the nozzle by an oxidizationtreatment. Further, a film obtained by using C₈F₁₇C₂H₄SiCl₃ was formedon the SiO₂ film. The evaluation results are shown in Table 2 below.

Comparative Example 3

An image was recorded and evaluated in substantially the same manner asthat in Example 1 except that the ink jet head 1 in Example 1 wasreplaced with the comparative head 3 which is constituted by having asilicon nozzle plate and does not have a rear flow path, that is to say,constituted with the common liquid chamber disposed at the same side asthe pressure chamber, and having a silicon nozzle plate with a platinglayer containing a fluorocarbon-based polymer formed by a eutectoidplating process.

Plural nozzles are provided in the silicon nozzle plate as shown inFIGS. 2 to 4, and ink droplets can be ejected with high precision asshown in FIG. 5. Further, the silicon nozzle plate is formed of singlecrystal silicon, and the surface of the silicon nozzle plate at a sidetoward the ink ejection direction of the nozzle is oxidized to have anSiO₂ film, and a plating layer containing fluorocarbon-based polymerformed as described below is provided on the SiO₂ film. The evaluationresults are shown in Table 2 below.

Formation of Plating Layer Containing Fluorocarbon-Based Polymer

The surface of SiO₂ film on the single crystal silicon was washed withan acid, and then, the single crystal silicon with the SiO₂ film wasimmersed in a liquid where a polytetrafluoroethylene particle(fluorocarbon-based polymer) is dispersed in a water solution containingnickel and cobalt as a matrix metal ion, the fluorocarbon-based polymerparticle was adhered on the surface of the SiO₂ film on the singlecrystal silicon through the matrix metal ion to form a coated film. Thecoated film was heated at 350° C. to form a plating film.

Comparative Example 4

An image was recorded and evaluated in substantially the same manner asthat in Example 4 except that the ink jet head 1 in Example 4 wasreplaced with the comparative head 3 which is constituted by having asilicon nozzle plate and does not have a rear flow path, that is to say,constituted with the common liquid chamber disposed at the same side asthe pressure chamber, and having a silicon nozzle plate with a platinglayer containing a fluorocarbon-based polymer formed by a eutectoidplating process.

Plural nozzles are provided in the silicon nozzle plate as shown inFIGS. 2 to 4, and ink droplets can be ejected with high precision asshown in FIG. 5. Further, the silicon nozzle plate is formed of singlecrystal silicon, and the surface of the silicon nozzle plate at a sidetoward the ink ejection direction of the nozzle is oxidized to have anSiO₂ film, and a plating layer containing a fluorocarbon-base polymerformed in substantially the same manner as that in Comparative Example 3is formed on the SiO₂ film. The evaluation results are shown in Table 2below.

Comparative Example 5

An image was recorded and evaluated in substantially the same manner asthat in Comparative Example 1 except that the ink jet head 1 inComparative Example 1 was replaced with the comparative head 3 which isconstituted by having a silicon nozzle plate and does not have a rearflow path, that is to say, constituted with the common liquid chamberdisposed at the same side as the pressure chamber, and having a siliconnozzle plate with a plating layer containing a fluorocarbon-basedpolymer formed by a eutectoid plating process in substantially the samemanner as that in Comparative Example 3.

Plural nozzles are provided in the silicon nozzle plate as shown inFIGS. 2 to 4, and ink droplets can be ejected with high precision asshown in FIG. 5. Further, the silicon nozzle plate is formed of singlecrystal silicon, and the surface of the silicon nozzle plate at a sidetoward the ink ejection direction of the nozzle is oxidized to have SiO₂film, and a plating layer containing the fluorocarbon-base polymerformed in substantially the same manner as that in Comparative Example 3is provided on the SiO₂ film. The evaluation results are shown in Table2 below.

Comparative Example 6

An image was recorded and evaluated in substantially the same manner asthat in Example 1 except that the ink jet head 1 in Example 1 wasreplaced with the comparative head 4 which has a configuration whichdoes not have a rear flow path, that is to say, a configuration wherethe common liquid chamber is disposed at the same side as the pressurechamber, where the nozzle plate is formed of a stainless steel alloy(SUS316L), and in which the nozzles are not arranged two-dimensionallyin a matrix. Further, there is a plating layer containing afluorocarbon-based polymer formed in substantially the same manner asthat in Comparative Example 3 on the surface of the silicon nozzle plateat a side toward the ink ejection direction of the nozzle. In thisregard, ejection conditions were changed to an ink droplet amount of 2.4pL, an ejection frequency of 25.7 kHz, and a resolution of 300 dpi×300dpi to record the image. The evaluation results are shown in Table 2below.

Comparative Example 7

An image was recorded and evaluated in substantially the same manner asthat in Example 1 except that colloidal silica used in ink preparationin Comparative Example 6 was not contained. The evaluation results areshown in Table 2 below.

TABLE 1 Comparative Comparative Head 1 Head 2 Head 3 Head 3 LquidRepellent C₈F₁₇C₂H₄SiCl₃ C₈F₁₇C₂H₄SiCl₃ Polytetrafluoro-Polytetrafluoro- Film ethylene ethylene Forming Method of ChemicalChemical Eutectoid Eutectoid Lquid Repellent Vapor Vapor Plating PlatingFilm Deposition Deposition Substrate of nozzle Silicon Silicon SiliconSUS plate Protective film of Silicon oxide Silicon oxide Silicon oxidenon nozzle plate Piezoelectric body disposed disposed disposed disposedTwo-dimensional arranged arranged non non matrix form Rear face flowpath adopted non non non design Resolution 1200 dpi 1200 dpi 1200 dpi300 dpi (single-pass) (single-pass) (single-pass) (single-pass)

TABLE 2 In Table 2, the abbreviation “Conternt*1” denotes “A content %by mass of the colloidal silica with respect to the total mass of theink composition”; and the abbreviation “S.L.R.F*2” denotes “State of theliquid repellent film”. Evaluation Colloidal Silica Image Image EjectionHead Inkjet Head Kind Conternt*1 Resin Particles Resolution DensityProperty Reliability S.L.R.F*2 Example 1 Head 1 used 0.05Self-dispersing AA AA AA AA AA Polymer Example 2 Head 1 used 1Self-dispersing AA AA B AA AA Polymer Example 3 Head 2 used 0.05Self-dispersing A A A AA AA Polymer Example 4 Head 1 used 0.05 EmulsionA AA AA AA AA polymerized Example 5 Head 2 used 0.05 Emulsion B B A AAAA polymerized Comparative Head 1 non 0 Self-dispersing AA AA AA D CExample 1 Polymer Comparative Head 2 non 0 Self-dispersing A A A C CExample 2 Polymer Comparative Comparative used 0.05 Self-dispersing A AB B B Example 3 Head 3 Polymer Comparative Comparative used 0.05Emulsion B B B B B Example 4 Head 3 polymerized Comparative Comparativenon 0 Self-dispersing A A B D D Example 4 Head 3 Polymer ComparativeComparative used 0.05 Self-dispersing C C B A B Example 6 Head 4 PolymerComparative Comparative non 0 Self-dispersing C C B A B Example 7 Head 4Polymer

As shown in Table 2, in Examples, the resolution and density of theimage and the head performance were good and deterioration of the liquidrepellent property of the liquid repellent film of the head plate wassuppressed, images of higher precision could be formed stably, while inComparative Examples 1, 2 and 5 not containing colloidal silica,deterioration of the liquid repellent property of the liquid repellentfilm was not suppressed, but the head reliability was reduced. Further,in Comparative Examples 6 to 7, the head material of the conventionalnozzle plates not using silicon was SUS, and therefore head reliabilitywas maintained, but the resolution of the nozzle arrangement itself wasnot increased and the resolution and density of the recorded image wereinsufficient.

Examples 6 to 10

An image was recorded and evaluated in substantially the same manner asthat in Examples 1 to 5 respectively except that magenta ink usedExamples 1 to 5 was changed to cyan ink individually.

As a result, in all Examples 6 to 10, deterioration of the head platewas suppressed in a manner substantially same as that in each ofExamples 1 to 5, and higher precise images were stably formed.

Examples 11 to 15

An image was recorded and evaluated in substantially the same manner asthat in Examples 1 to 5 respectively except that colloidal silica (tradename SNOWTEX XS) used in Examples 1 to 5 was replaced with sodiumsilicate individually.

As a result, deterioration of head plate was suppressed in a mannersubstantially same as that in each of Examples 1 to 5, and higherprecise images were stably formed.

The invention provides an image forming method and an ink compositionwhereby deterioration of the liquid repellent property of the inkjethead member can be suppressed and higher precise images can be stablyformed.

The foregoing description of the exemplary embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. The embodiments were chosenand described in order to best explain the principles of the inventionand its practical applications, thereby enabling others skilled in theart to understand the invention for various embodiments and with thevarious modifications as are suited to the particular use contemplated.

All publications, patent applications, and technical standards mentionedin this specification are herein incorporated by reference to the sameextent as if such individual publication, patent application, ortechnical standard was specifically and individually indicated to beincorporated by reference. It will be obvious to those having skill inthe art that many changes may be made in the above-described details ofthe preferred embodiments of the present invention. It is intended thatthe scope of the invention be defined by the following claims and theirequivalents.

What is claimed is:
 1. An image forming method comprising ejecting anink composition comprising an inorganic silicate compound from an inkjethead having a nozzle plate to form an image, the nozzle plate comprisinga liquid repellent film, and the liquid repellent film comprising afluoroalkylsilane moiety, wherein a content of the inorganic silicatecompound in the ink composition is in a range of from 0.0005% by mass to0.5% by mass with respect to a total mass of the ink composition.
 2. Theimage forming method according to claim 1, wherein the liquid repellentfilm comprising a fluoroalkylsilane moiety is formed by using a compoundrepresented by the following Formula (1):C_(n)F_(2n+1)—C_(m)H_(2m)—Si—X₃  Formula (1) wherein, in Formula (1), nrepresents an integer of 1 or more; m represents an integer of 0 ormore; X represents an alkoxy group, an amino group, or a halogen atom;and a part of X may be substituted with an alkyl group.
 3. The imageforming method according to claim 2, wherein the liquid repellent filmis formed by chemical vapor deposition.
 4. The image forming methodaccording to claim 2, wherein at least a part of the nozzle platecomprises silicon.
 5. The image forming method according to claim 2,wherein the nozzle plate has plural ejection ports which eject the inkcomposition, the inkjet head further comprises plural pressure chambersrespectively communicating with the plural ejection ports of the nozzleplate, plural ink supply flow paths respectively supplying the inkcomposition to the plural pressure chambers, a common liquid chambersupplying the ink composition to the plural ink supply flow paths, andplural pressure generation units respectively deforming the pluralpressure chambers, and an amount of change in volume within eachpressure chamber is controlled by driving the respective pressuregeneration unit to eject the ink composition.
 6. The image formingmethod according to claim 5, wherein the pressure generation units arepiezo elements.
 7. The image forming method according to claim 5,wherein the plural ejection ports are arranged two-dimensionally in amatrix form.
 8. The image forming method according to claim 5, whereinthe inkjet head further comprises electrical wiring which is arranged soas to penetrate the common liquid chamber and supplies driving signalsto the pressure generation units.
 9. The image forming method accordingto claim 8, wherein the pressure generation units are disposed on theopposite side of the pressure chamber from a side thereof where thenozzle plate is arranged, and the common liquid chamber is disposed onthe opposite side of the pressure generation units from a side thereofwhere the pressure chambers are arranged.
 10. The image forming methodaccording to claim 2, wherein the ink composition further comprises apigment, a water-soluble organic solvent, and resin particles.
 11. Theimage forming method according to claim 10, wherein the resin particlesare self-dispersing polymer particles.
 12. The image forming methodaccording to claim 2, wherein the inorganic silicate compound iscolloidal silica.
 13. An ink composition comprising an inorganicsilicate compound and being used for the image forming method accordingto claim 2.